It was not until dark he found he thought was the correct way to solve the problem.
| A．that; what | B．that; that | C．when; what | D．when; that |
The roommates have lived for three years and not once _____with each other.
| A．they had quarreled | B．they have quarreled |
| C．have they quarreled | D．had they quarreled |
My hometown, _____I spent my happy childhood, has changed a lot.
| A．when | B．where | C．which | D．since |
_____that the girl with an incurable disease would die soon, the boy decided to help her make her last days beautiful and meaningful.
| A．Being found out | B．Found out | C．To find out | D．Having found out |
Exploring _____space is exciting, yet dangerous.
There is _____need for both robots and humans for space exploration.
| A．the; a | B．a; a | C．/; a | D．/; the |
Life is like time. Once _____, it never returns.
| A．to lose | B．losing | C．lost | D．being lost |