They’ve made full preparations but it remains whether they will be able to do a good job

问题补充：

They’ve made full preparations, but it remains whether they will be able to do a good job in the experiment.

A. to see

B. seen

C. being seen

D. to be seen

答案：

A. to see

B. seen

C. being seen

(答案→)D. to be seen

解析：考查不定式的被动做表语：句意：他们已经做好准备了，但是是否在实验中能做得好还又待证实。It remains to be seen whether…，是否…还有待证实，这里不定式的被动做表语，选D。