He ____ a machine the last time we saw him.A.was operating on B.was operating Why 这2个区别?
问题描述：
He ____ a machine the last time we saw him.
A.was operating on B.was operating
Why 这2个区别?
答
operating是及物动词，不用加介词on
答
及物动词 vt.
1.操作;开动(机器)等
Who operates that machine?
那台机器由谁操作?
答
operate sth
操纵某物
operate on sth
给……做手术
这样明白了吧?怎么能给机器做手术呢?所以答案是B