s a wide ________of reference books to be found, so ________you look for somematerial needed, you can turn to me.

What can trees do _________ us — They can _________ harmful gases and produceoxygen .

Do you know who took the students to the old people’s home, Tony—Well, Mr. Smith _______.

I haven’t finished my homework yetI my mother with the housework all day yesterday

I never thought she would ________ my invitation(邀请) to the theatre.— She will feel sorry for missing the theatre some day.