21. ________your generous help, we could not be living a happy life today.
A. Despite B. But for C. Because of D. As long as
22. They have been woking on this project for one month. It seems they need ________ month to finish it.
A. more B.other C. another D. the other
23. Many people believe that _______ will takes years to develop a car that does not pollute the air.
A. it B. that C. there D. this
24.______ the beginning of the 19th century did scientists know that all matter is made up of atoms.
A. At B. By C. Up to D. Not until
