Although the causes of cancer _____, we do not yet have any practical way to prevent it.
| A．are being uncovered |
| B．have been uncovering |
| C．are uncovering |
| D．have uncovered |
______in four different countries, Jessie is a typical third culture kid, the term of which refers to children who spend a period of time in one or more cultures．
| A．Bring up | B．Having brought up |
| C．Bringing up | D．Brought up |
The Mekong River Commission has found no evidence ______ the dams on the upper reaches have an influence on the water flow downstream．
| A．which | B．that | C．where | D．what |
Head coach Li Yan bursts into tears of joy when she sees Zhou Yang first _____ the finish line at the women's 1500m short track speed skating final．
| A．to cross | B．having crossed | C．cross | D．crossed |
27．It was the President himself______ opened the door．
| A．who | B．when | C．which | D．where |
The actor still remembers the excitement in his class when a female classmate _____ for a key role in a Zhang Yimou film．
| A．is chosen | B．s chosen | C．chooses | D．chose |