Over the past decades , sea ice in the Arctic as a result of global warming .
| A．had decreased | B．decreased | C．has been decreasing | D．is decreasing . |
Not until he left his hometo know how important the family was for him.
| A．did he begin | B．had he begun |
| C．he began | D．he has begun |
—Did you enjoy yourself last night?
—Yes, it’s very nice of you. I appreciatedto the party.
| A．to be invited | B．to have invited |
| C．having been invited | D．having invited |
The cost of renting a house in central Chengdu is higher than in any other area of the city.
| A．it | B．one | C．that | D．ones |
After completing and signing it, please return the form to us in the envelope .
| A．providing | B．provided |
| C．having provided | D．being provided |
Some insects the color of their surroundings to protect themselves.
| A．take in | B．take off |
| C．take on | D．take up |