The children are seldom encouraged up late at night preparing their lessons if .A. staying

问题补充：

The children are seldom encouraged up late at night preparing their lessons,if .

A. staying;once

B. to stay;ever

C. staying;sometimes

D. to stay;never

答案：

A. staying;once

(答案→)B. to stay;ever

C. staying;sometimes

D. to stay;never

解析：encourage sb. to do sth. 鼓励某人做某事；if ever 如果有。