---What are you busy with ?--- We are carrying out a research _______ the causes of cancer.
A good teacher should encourage his students to __________ the knowledge by themselves instead of just copying and memorizing what the teacher said in class.
—Could I ask you a rather personal question? —Sure, __________.
People try to avoid public transportation delays by using their own cars, and this __________ creates further problems.
The __________ look on his face showed that he hadn't expected it.
You didn't use to like him much when we were at school, __________?