Is that _________ sister, Dave? — No, it isn’t. She is my friend.

Do you know Jack well? —- Certainly, we _________ friends since ten years ago.

______ people have become masters of their country ____ science can really serve the people.

His grandparents ______ Hangzhou for 40 years. They like living there.

I knocked on the door several times but answered, so I left.