According to the author, the development of the highly specialized technology, for space travel has not only made space travel possible but also _______.

A．The man was badly hurt.
B．He had a terrible accident and had his left leg broken.
C．Two racing cars collided.
D．Two racing drivers were killed.

A．He relaxes.
B．He goes fishing.
C．He goes to work.
D．He works at home.