Believe it or not, he was seen ______upstairs just now. A. to go B. to going C. having gone D. go 答案:A 解析: see, watch, look at ,feel, notice, observe, listen to, hear 等感官动词(短语)及make, let, have等役使动词后用不带to的不定式作宾补,但这类结构变成被动语态时,to 不可以省略另外,在感官动词后也可用现在分词作宾补,但其意义表示动作正在进行。如:I saw him running after the bus.(动作正进行)行驶中的汽车遇到紧急情况急刹车时,由于具有 ,仍会向前滑行.汽车在淋湿的路面上行驶,交通事故要多些,原因是汽车所受到的摩擦力 (填“较大”或“较小”),容易打滑.