当水平梁上铅垂平面发生平面弯曲时，如某横截面的弯矩为负值，则该横截面上正应力的正确分布图是

A、<IMG src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/staticQuestionImg/dff428e5-9bec-4cfc-84a9-b9eef0ece8c0.png"title="ex_1397114510773_0.png" alt="ex_1397114510773_0.png"/>

B、<IMG src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/staticQuestionImg/5805ed80-d93d-43d4-aeb5-06fc56154a3e.png"title="ex_1397114538099_0.png" alt="ex_1397114538099_0.png"/>

C、<IMG src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/staticQuestionImg/c1637201-b8b4-4dc0-98d0-ec80571c5d2f.png"title="ex_1397114561236_0.png" alt="ex_1397114561236_0.png"/>

D、<IMG src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/staticQuestionImg/dfe47367-005d-4c8a-86a3-7be72797dc71.png"title="ex_1397114607149_0.png" alt="ex_1397114607149_0.png"/>