1 . A number of experts ________ (invite) to attend the meeting last week. (所给词的适当形式填空)

2 . Early this morning, bright lights ________ (see) in the sky outside the city. (所给词的适当形式填空)

3 . Inca builders cut stones to exact sizes so that nothing ________ (need)to hold walls together other than the perfect fit of the stones. (所给词的适当形式填空)

4 . Thousands of foreigners ____________ (attract) to the Shanghai World Expo the day it opened. (所给词的适当形式填空)