When I got into the classroom, I found abook ______ on the floor.

we have done a lot to build a low-carbon economy,yet it is still _________ ideal. We have to work even harder.

There ______ two English lessons tomorrow, please prepare for them.

elevision was first introduced, the extent_______ it would affect society could not have been foreseen.

Please do me a favor — ______ my friend MrSmith to Youth Theater at 7:30tonight