This machine is very easy . Anybody can learn to use it in a few minutes. A. operating B.

This machine is very easy . Anybody can learn to use it in a few minutes.
A. operating
B. to be operating
C. operated
D. to operate

A. operating B. to be operating C. operated (答案→)D. to operate解析：考查非谓语动词的区别。一些表示状态性质的形容词比如：easy；hard；comfortable等用来作表语时，sth作为主语，形容词后面接动词不定式，该不定式动词如果是及物动词与句子主语构成动宾关系;例如：My homework is easy to finish. 如果形容词后面接的动词不定式的动词是vi，则动词后面带介词后仍然跟句子主语之间构成动宾关系；例如; The room is comfortable to live in. 句意：这台机器很容易操作。任何人都可以在几分钟内学习使用它。故D 正确。

和我的回答一样，看来我也对了