It never _____ humans until the mid1990s that some animals can be cloned.
| A．occur | B．is occurred | C．occurred to | D．occurred |
It’s said that he’s looking for a new job, one ______ he can get more money to support his family.
| A．when | B．where | C．that | D．which |
When he was working there he caught a serious illness from _____ efforts he still suffers.
| A．which | B．that | C．whose | D．what |
Luckily, we’d brought a road map without ______ we would have lost our way.
| A．it | B．that | C．this | D．which |
In the office I never seem to have time until after 5:30 pm, _____ many people have gone home.
| A．that | B．which | C．whose time | D．by which time |
All of the flowers now raised here have developed from those _______ in the forest.
| A．once they grew | B．they grew once | C．they once grew | D．once grew |