由于（）的存在，使各层注水受效程度不同，造成各层油层压力和含水率相差悬殊。
A、层内矛盾
B、平面矛盾
C、层间矛盾
D、开发矛盾
参考答案：C
Do you still remember the key points that ___________ in his report? I don’t remember them all.
A．referred to
B．were referred
C．he was referred to
D．were referred to
在深度为5的满二叉树中，叶子结点的个数为
A．31
B．32
C．16
D．15
