西北地区的主要地形是（　　）

A．平原和山地

B．丘陵和平原

C．高原和盆地

D．高原和丘陵

阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用

括号中词语的正确形式填空。

     Do you feel 1._____ difficult to be happy all the time? Now I'll give you some tips 2._____ how to make

yourself happy. One way is being unselfish because 3._____ (self) is the key factor 4._____ (require) if you

want to get along well with others. By 5._____ (say) being unselfish we mean we should not want everything

our own way or demand the best share of everything. 6._____ way is to look for good points in other people.

You'll find most people pleasant to go with and it will surely make you happy. Third, you can not expect to be

too perfect, 7._____ don't be too unhappy when you make a mistake. Everything will be OK if you try to make

things right. Finally, it is important to remember 8._____ while you are no 9._____ (bad) than others, chances

you have may not be much better. In this case, 10._____ surest way to be happy is to think yourself above

other people.