―Would you like to visit the new museum with us this Sunday?―____________, but I will have to work then.
I couldn’t ____. The line was busy.
The conference has been held to discuss the effect of tourism(旅游业) ___ the wildlife in the area.
Sandra was a student ____ the age of 21.
Scientists say they are beginning to _____ in the fight against cancer.
As the spring comes, the flowers began to _____.