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>Researchers studying vision use various methods to investigate human perceptual experience. Research on spectral sensitivity of the rod receptors (scattered throughout the retina) and cone visual receptors (mainly concentrated in the fovea area of the retina) highlights the relationship between perception and physiology. Signal detection methods have been used to measure the differences in how perception adjusts to low-light environments. Participant responses can be plotted based on sensitivity versus length of time in the dark. The dark adaptation curve can be plotted showing how rods and cones differ in their sensitivity to light over time. The following graph shows a plot of three calculated dark adaptation curves. <image 1> Which of the following statements is true?
A. Rods are responsible for color vision, which explains color sensitivity under low-light conditions.
B. Cones are responsible for color vision, which explains greater color sensitivity under low-light conditions.
C. Rods do not respond preferentially to wavelengths in the light spectrum, which explains why colors are not detectable in low-light conditions.
D. Both rods and cones respond to specific colors in the light spectrum; loss of color vision in dark conditions is the result of fewer photons of light.

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
Researchers studying vision use various methods to investigate human perceptual experience. Research on spectral sensitivity of the rod receptors (scattered throughout the retina) and cone visual receptors (mainly concentrated in the fovea area of the retina) highlights the relationship between perception and physiology. Signal detection methods have been used to measure the differences in how perception adjusts to low-light environments. Participant responses can be plotted based on sensitivity versus length of time in the dark. The dark adaptation curve can be plotted showing how rods and cones differ in their sensitivity to light over time. The following graph shows a plot of three calculated dark adaptation curves. <image 1> Which of the following statements is true?
A. Rods are responsible for color vision, which explains color sensitivity under low-light conditions.
B. Cones are responsible for color vision, which explains greater color sensitivity under low-light conditions.
C. Rods do not respond preferentially to wavelengths in the light spectrum, which explains why colors are not detectable in low-light conditions.
D. Both rods and cones respond to specific colors in the light spectrum; loss of color vision in dark conditions is the result of fewer photons of light.

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