Stephen Hawking has expressed his opinion humans might one day be able to make spaceships capable of such speeds that time on board would slow down．
A. that
B. whom
C. which
D. what
网友回答
(答案→)A. that
B. whom
C. which
D. what
解析：考查名词性从句。句中考查that引导的同位语从句，解释说明名词his opinion，在句中不作任何成分，故选A。