一、根据句意及所给首字母或中文提示,完成下列句子
1.He asked_________(是否)they needed some more books or not.
2.Anything that is dropped falls towards the ground because of the force of_________(重力).
3.Some scientists do not believe that the_________(旅程)to Mars will be very comfortable.
4.About four-________(五)of the books in our 1ibrary are written in Chinese.
5.It’s c________ that every effect must have a cause.