I’ve kept up a friendship with a girl whom I was at school ________ twenty years ago.
The surface of the table ______ smooth enough.
At last,we found ourselves in a pleasant park ________trees providing shade(荫凉)and sat down to eat our picnic lunch.
.Manufacturers should have professional productivity and technical knowledge to ______ the quality of the products.
.It was in the 1990s _______ we were working together ____ we made friends with each other.
—Tom, help me buy two tickets for this weekend’s concert online.—Sorry, there is no ticket _______ online now.