Ladies and gentlemen，please fasten your seat belts．The plane       ．

Many a student ______ made that mistake before, which is another way of saying a great many students ________ made that mistake.

—How long have you retired, Grandpa?—Well, four years, But you know, I         for Courtaulds for over forty years.

—What’s that terrible noise?—The neighbors      for a party. 

With the rapid development of medical science, we ________ more new drugs used in the treatment of cancer.