The lake looks in the moonlight and we can hear insects (昆虫) sing .

Look at the young lady in red. Is it Mrs. King?—No, It ________ be her. She is wearing a white dress today.

After Mandela was free (自由的) in 1990, he chose to shake hands with the people ________ wanted to kill him.

You ought to have put the milk in the refrigerator, and now ________sour.

The book ________ be Tom’s. Look! His name is on it.