Stephen Hawking believes that the earth is unlikely to be the only planet life has developed gradually.
A. that
B. where
C. which
D. whose
网友回答
A. that
(答案→)B. where
C. which
D. whose
解析：考查定语从句：先行词是the only planet，定语从句缺少地点状语，用where引导定语从句，句意：Stephen Hawking认为地球不可能是生命逐渐发展的唯一星球。选B.