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><image 1> The diagram above represents the idealized titration curve for the reaction of sodium oxalate ($Na_2C_2O_4$) with a strong acid like hydrochloric acid ($HCl$). E and F represent the pH at the endpoints. G and H will depend on the composition of the sample with the possibility that one may not be present. In addition to water, what are the predominant species in solution at E?
A. $Na_2C_2O_4$ and $HCl$
B. $Na^+$, $Cl^-$, and $HC_2O_4^-$
C. C_2O_4^{2-} and $H^+$
D. $Na^+$, $H^+$, and $C_2O_4^{2-}$

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
B
<image 1> The diagram above represents the idealized titration curve for the reaction of sodium oxalate ($Na_2C_2O_4$) with a strong acid like hydrochloric acid ($HCl$). E and F represent the pH at the endpoints. G and H will depend on the composition of the sample with the possibility that one may not be present. In addition to water, what are the predominant species in solution at E?
A. $Na_2C_2O_4$ and $HCl$
B. $Na^+$, $Cl^-$, and $HC_2O_4^-$
C. C_2O_4^{2-} and $H^+$
D. $Na^+$, $H^+$, and $C_2O_4^{2-}$

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