Half an hour has been made full of the problem.
A. using; studying
B. use; to study
C. to use; to study
D. use; studying
网友回答
A. using; studying
(答案→)B. use; to study
C. to use; to study
D. use; studying
解析：考查固定词组和句子结构。固定词组make full use of充分利用，本句是被动语态；第二空的不定式做目的状语。句意：半个小时已经被充分利用了来研究这个问题。故B正确。