The eighteenth and nineteenth centuries ________ the widespread use of electricity and the birth of the steam engine, leading to the development of factories and cities．

1. A.
   watched
2. B.
   observed
3. C.
   saw
4. D.
   showed

The eighteenth and nineteenth centuries _____ the widespread use of electricity and the birth of the steam engine , leading to the development of factories and cities.

A. watched             B. observed        C. saw                   D. showed

The eighteenth and nineteenth centuries _____ the widespread use of electricity and the birth of the steam engine , leading to the development of factories and cities.

A．watched

B．observed

C．saw

D．showed