Answer :
The question is asking about the duration of time someone has been studying Chinese. The correct choice from the given options is B. 'how long'. This is because 'how long' specifically asks about the duration or length of time something has been happening.
Explanation:
Option A: 'how often' - This option asks about the frequency with which an activity is done. It would be correct in a sentence where someone wants to know how frequently you study Chinese (e.g., daily, weekly).
Option B: 'how long' - This is the correct choice because it inquires about the duration, i.e., the total time span during which you have been studying Chinese. For instance, an appropriate answer might be 'I have been studying Chinese for two years.'
Option C: 'how many' - This option is used to ask about the number of items or people. It wouldn't relate correctly to the question about the duration of study.
Option D: 'how does' - This option asks about the way or manner in which something is done, which doesn’t relate to the duration of study.
Thus, the most suitable answer to complete the sentence is 'how long have you been studying Chinese?' This helps the question ask for a specific duration, implying a need for an answer that indicates how much time has been invested in learning the language.