The school has developed an on­line system________students can choose their own teachers.

The suspect’s fingerprint printed on the gun was themain __________ against him

— This kind of food is said to contain poisonous chemicals. — So why not _____ it?

He sent me an e-mail, _______ to getfurther information.

I will miss my family when I go abroad for further study next year.—-Don’t worry. You can ________ them by email.