__ carefully if any change occurs when doing experiments in the lab..

A. ObserveB. To observe

C. Observed D. Observing

Last night, there were millions of people _______ the opening ceremony live on TV.

A. watchB. to watch

C. watchedD. watching

I borrow the book Sherlock Holmes from the library last week, ______ my classmates recommended to me..

A. whoB. which

C. when D. Where

________ I have a word with you? It won’t take long.

A. CanB. Must

C. ShallD. Should

There are still many problems ______ before we are ready for a long stay on the Moon.

A. solvingB. solved

C. being solvedD.to be solved

_______ the forest park is far away, a lot of tourists visit it every year.

A. AsB. When

C. Even thoughD. In case

The best moment for the football star was _______ he scored the winning goal.

A. where B. when

C. how D. why

--- What time is it?

--- I have no idea. But just a minute, I ______ it for you.

A. checkB. checked

C. will checkD. would check

I found the lecture hard to follow because it _______ when I arrived.

A. startedB. was starting

C. would startD. had started

Some people believe _______ has happened before or is happening now will repeat itself in the future.

A. whateverB. whenever.

C. whereever D. however