You can come here to ask me ________ if you have any questions.
I shall never forget those years ________I lived in the country with farmers, ________has a great effect on my life.
________ many times,I still didn't know how to operate the machine.
Tony is said ________ to New York, and now he is studying medicine in a famous college in America.
Today the Red Cross provides a number of services for the public, such as helping people________, teaching first aid and providing blood.
Everyone in the class is expected to________in the discussion.