When asked to explain ____ made her remain so young , she began to tell us her secret.

It _______ ten years since my sister ______ an English teacher.

He ______ the key, so we ______ into the office.

uncertain sideeffect the medicine will bring about , though about one thousand patients havetaken it.

Look at the students in Grade 7, they look ______ cooler in military uniform(军服).— I agree with you, they look smart.