If nature does not provide man with the necessary material, it is the laboratory he will turn to for it．
A. where
B. that
C. which
D. what
网友回答
A. where
(答案→)B. that
C. which
D. what
解析：考查强调结构。本句结构为it is + 强调部分 + that从句，强调the laboratory，在句中作turn to的宾语，选B。