Ann is so careful that she always goes over her exercises to _______ there are no mistakes.
| A．look for | B．make sure | C．find out | D．think about |
All efforts of cloning an animal will be ________ if there is not enough diversity in the group to overcome illness.
| A．in need | B．in place | C．in vain | D．in case |
It was the building of the rail network from the west to the east coast ________ brought even larger numbers to California in the 1860s.
| A．that | B．what | C．how | D．which |
_______ from the top of the mountain, we found the city more beautiful.
| A．Seen | B．Having been seen | C．Seeing | D．Being seen |
Do you know the stages every inventor must ________ before they can have their invention________ .
| A．go through; approve | B．go through; approved |
| C．get through; approval | D．look through; approved |
The dodo became extinct fairly recently so its DNA is still ________ .
| A．in good condition | B．in good state |
| C．in good conditions | D．out of a condition |