题目

It is well understood _____ controls the flow of carbon dioxide in and out the atmosphere today. A. that    B. when  C. what   D. how 答案：C有一长方体木块，分别以图甲和乙两种方式漂浮在水面上，若木块底部受到水的压力分别为F甲和F乙，则（　　）A．F甲＞F乙B．F甲=F乙C．F甲＜F乙D．条件不足，无法比较