The students _____ busily when Miss Brown went to get a book she ____ in the office.
By the middle of the 21st century, the vast majority of the world’s population _____ in cities rather than in the country.
--- I need to advertise for a roommate for next term. --- _____? Mary is interested.
A major earthquake _____ 8.0 on the Richter scale strongly _____ Wenchuan County in Sichuan Province at 2:28 p.m. on May 12, 2008.
It was in the small house _____ was built with stones by his father _____ he spent his childhood.
--- May I go and play with Dick this afternoon, Mum? --- No, you can’t go out _____ your work is being done.