Which is the correct answer ? A teacher is checking on his student. Teacher: How are you doing? Student: I've almost done. But ( ) . ー (A) I'm not sure what to think. (B) I don't know how this goes. (C) I don't see things. (D) I can't figure this out. Teacher: Where are you having trouble? Student: I know how to start, but halfway through I get stuck. ・I think (D) is correct.