You are a helpful assistant. When the user asks a question, your response must include two parts: first, the reasoning process enclosed in <think>...</think> tags, then the final answer enclosed in <answer>...</answer> tags.Please provide a clear, concise response within <answer> </answer> tags that directly addresses the question.
system
<image>The cardiovascular protective effects of fruit intake have been widely demonstrated in Western populations, but little is known about the association in China, where fruit intake levels are low and the incidence of stroke is high. To investigate whether this association also exists in the Chinese population, the University of Oxford (UK), in collaboration with Professor Li Liming's group at the Chinese Academy of Medical Sciences (CAMS), recruited 512,891 adults aged 30-79 years from 10 different regions of China (including five cities and five villages) between June 2004 and July 2008, to investigate the association between the use of fresh fruits and major cardiovascular diseases in the Chinese population. The study investigated the relationship between fresh fruit use and major cardiovascular diseases in the Chinese population. Five frequency criteria were set for the main exposure factor "fruit intake": "never eat fruit", "once a month", "1-3 times a week", "4-6 times a week", "every day ", which were filled in by the respondents themselves.The primary cardiovascular disease death was used as the outcome event in this study. Survival and health status of all subjects were regularly reported to the disease surveillance system of the Chinese Centre for Disease Control and Prevention (CDC), and their data were checked against the health insurance records of the investigated subjects' localities and confirmed by the street or village committees. Coding was based on the 10th edition of the International Classification of Diseases.After 3.2 million person-years of follow-up, a total of 451,665 subjects completed the follow-up after excluding lost and ineligible subjects. Those who consumed fresh fruit daily were found to have a mean reduction in systolic blood pressure of about 4 mmHg, a reduction in blood glucose of about 0.5 mmol/L, a 40% reduction in the risk of cardiovascular death, and a 34%, 25%, and 36% reduction in the risk of major coronary heart disease events, ischemic strokes, and cerebral hemorrhages, respectively, when compared with those who consumed very little fresh fruit. Their fruit intake and cardiovascular disease profiles were shown in the table below.<image 1>What indicators were appropriate for describing the risk of morbidity in various groups of the population?
A. point prevalence and period prevalence
B. mortality rate and case fatality rate
C. cumulative incidence and incidence density
D. PYLL and DALY

Please answer the question with option letter from given choices in the format of Answer: <option letter>. You FIRST think about the reasoning process as an internal monologue and then provide the final answer. The reasoning process MUST BE enclosed within <think> </think> tags. Please answer the final answer within the <answer> </answer> tags.
user
C
The cardiovascular protective effects of fruit intake have been widely demonstrated in Western populations, but little is known about the association in China, where fruit intake levels are low and the incidence of stroke is high. To investigate whether this association also exists in the Chinese population, the University of Oxford (UK), in collaboration with Professor Li Liming's group at the Chinese Academy of Medical Sciences (CAMS), recruited 512,891 adults aged 30-79 years from 10 different regions of China (including five cities and five villages) between June 2004 and July 2008, to investigate the association between the use of fresh fruits and major cardiovascular diseases in the Chinese population. The study investigated the relationship between fresh fruit use and major cardiovascular diseases in the Chinese population. Five frequency criteria were set for the main exposure factor "fruit intake": "never eat fruit", "once a month", "1-3 times a week", "4-6 times a week", "every day ", which were filled in by the respondents themselves.The primary cardiovascular disease death was used as the outcome event in this study. Survival and health status of all subjects were regularly reported to the disease surveillance system of the Chinese Centre for Disease Control and Prevention (CDC), and their data were checked against the health insurance records of the investigated subjects' localities and confirmed by the street or village committees. Coding was based on the 10th edition of the International Classification of Diseases.After 3.2 million person-years of follow-up, a total of 451,665 subjects completed the follow-up after excluding lost and ineligible subjects. Those who consumed fresh fruit daily were found to have a mean reduction in systolic blood pressure of about 4 mmHg, a reduction in blood glucose of about 0.5 mmol/L, a 40% reduction in the risk of cardiovascular death, and a 34%, 25%, and 36% reduction in the risk of major coronary heart disease events, ischemic strokes, and cerebral hemorrhages, respectively, when compared with those who consumed very little fresh fruit. Their fruit intake and cardiovascular disease profiles were shown in the table below.<image 1>What indicators were appropriate for describing the risk of morbidity in various groups of the population?
A. point prevalence and period prevalence
B. mortality rate and case fatality rate
C. cumulative incidence and incidence density
D. PYLL and DALY

Please answer the question with option letter from given choices in the format of Answer: <option letter>. You FIRST think about the reasoning process as an internal monologue and then provide the final answer. The reasoning process MUST BE enclosed within <think> </think> tags. Please answer the final answer within the <answer> </answer> tags.
val