单选题 If nature does not provide man with the necessary material, it is the laboratory ______ he will turn to for it.
A. where B. which C. that D. what

【正确答案】 C
【答案解析】本题考查强调句的用法，强调句型的结构是：“It is/was+被强调的部分+ that/who/whom+句子的其他部分”。