I’m impressed with his determination. When he had a problem to solve, he  _____ work at it until he found an answer.

______ I see your ID card, sir? We have to check your information.

 —Mom, I did not pass the exam.—What a pity! You     it.

According to common practice, the president _________ hold office for five years.

---Look at that girl! Is that Susan?---No , it _______ be her. She has gone back to her hometown.