In January, 2004, the United States successfully launched “Spirit”, a Mars Exploration Rover, _____ a new milestone in the history of mankind.
| A．it marked | B．marking | C．marked | D．to mark |
I was really too busy with my homework and I couldn't help ____________ housework.
| A．doing | B．do | C．did | D．done |
Mary is one of the brightest students who_________ from New York University.
| A．is graduated | B．have graduated |
| C．has graduated | D．are graduated |
Mr. Alcott, headmaster of the school, refused to accept made by the Students' Union.
| A．either | B．neither | C．any | D．none |
Mary is short__________ her brother is very tall.
| A．still | B．nor | C．while | D．when |
There was less food for birds and also for the Prairie dog, an______holes in the ground.
| A．livs | B．is living | C．living | D．lived |