题目

______some people are motivated by a need for success, others are motivated by a fear of failure. A . Because B . If C . Unless D . While 答案：D(x+1)(x+2)>0是(x+1)(+2)>0的（     ）条件 A．必要不充分      B．充要       C．充分不必要     D．既不充分也不必要