第11题: [单项选择]All flights ______because of the snowstorm, many passengers could do nothing but take the train. A. had been canceled B. have been canceled C. were canceled D. having been canceled 参考答案:D 答案解析:该题为“逻辑主语+doing”构成主语独立结构,表示原因。
第17题: [单项选择]用手握住瓶子,使瓶子在竖直方向静止,如果握力加倍,则手对瓶子的摩擦力() A. 握力越大,摩擦力越大。 B. 只要瓶子不动,摩擦力大小不变。 C. 方向由向下变成向上。 D. 手越干越粗糙,摩擦力越大。 参考答案:B 答案解析:试题分析:瓶子保持静止,受力平衡,对瓶子受力分析,竖直方向上受重力和静摩擦力,二力平衡,因而静摩擦力等于重力;握力加倍后,瓶子更掉不下,依然保持静止,竖直方向上重力和静摩擦力依然平衡,静摩擦力还是等于