Those children don’t have to learn for they always work hard voluntarily.A. make to B.

问题补充：

Those children don’t have to learn , for they always work hard voluntarily.

A. make to

B. be made

C. make them

D. be made to

答案：

A. make to

B. be made

C. make them

(答案→)D. be made to

解析：考查固定结构。固定结构make sb do sth让某人做某事；在do前面省略不定式符号to,该结构在变成被动语态的时候，要把不定式符号to加上去，形成be made to do sth；句意：不必让那些孩子去学习，因为他们一直学习得都很自觉。故D正确。