An ecosystem consists of the living and nonliving things in an area __________ interact(互相作用) with one another.
| A．that | B．where | C．who | D．what |
. In April, thousands of holidaymakers remained abroad due to the volcanic ash cloud.
:
| A．sticking | B．stuck | C．to be stuck | D．to have stuck |
.Lots of rescue workers were working around the clock ,supplies to Yushu, Oinghai province after the earthquake.
| A．sending | B．to send | C．having sent | D．to have sent |
. Listen! Do you hear someone __________for help?
| A．calling | B．call | C．to call | D．called |
Dina, _______ for months to find a job as a waitress, finally took a position at a local advertising agency.
| A．struggling | B．struggled | C．having struggled | D．to struggle |
. So far nobody has claimed the money ___________________in the library.
| A．discovered | B．to be discovered | C．discovering | D．having discovered |