In fact, to solve this logical problem, the key point is to analyze each condition first. Proposition a indicates that the sine function is not equal to this value, and proposition b indicates the angle at which the sine function is not equal to this value in the case of proposition a.

Answer to this question: Choose A. Reason: In the case of proposition A, the angle of proposition B is 120 degrees or 60 degrees, so. It is enough to deduce B from A. On the other hand, when deducing A from proposition B, it can be equal to 60 degrees because it is not equal to 120 degrees, and the result of 60 degrees does not meet the condition of A. 。