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>Hint: Please answer the question and provide the correct option letter, e.g., A, B, C, D, E, at the end.
Question: In the quadrilateral $\mathrm{ABCD}, \mathrm{AD}=\mathrm{BC}, \angle \mathrm{DAC}=50^{\circ}$, $\angle \mathrm{DCA}=65^{\circ}$ and $\angle \mathrm{ACB}=70^{\circ}$. How big is $\angle \mathrm{ABC}$?
<image1>
Choices:
(A) $50^{\circ}$
(B) $55^{\circ}$
(C) $60^{\circ}$
(D) $65^{\circ}$
(E) It is not clear. 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
B
Hint: Please answer the question and provide the correct option letter, e.g., A, B, C, D, E, at the end.
Question: In the quadrilateral $\mathrm{ABCD}, \mathrm{AD}=\mathrm{BC}, \angle \mathrm{DAC}=50^{\circ}$, $\angle \mathrm{DCA}=65^{\circ}$ and $\angle \mathrm{ACB}=70^{\circ}$. How big is $\angle \mathrm{ABC}$?
<image1>
Choices:
(A) $50^{\circ}$
(B) $55^{\circ}$
(C) $60^{\circ}$
(D) $65^{\circ}$
(E) It is not clear. 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