现阶段我国工程建设监理活动主要在工程建设项目的( )阶段开展。 A．决策 B．设计

把下列各式分解因式：

（1）3a（x-y）-5b（y-x）

（2）a⁴-1

（3）-b³+4ab²-4a²b．

(2013·中原名校联考)Not only ________ polluted but also ________ crowded.

A．is the city；are the streets

B．the city is；the streets are

C．is the city；the streets are

D．the city is；are the streets

I am cooking _______ they are setting the table. [ ]

A. but

B. then

C. because

D. while

In our school there ______ a number of books on science and the number of them ______ growing larger and larger.

A．is; are

B．are; is

C．are; are

D．is; is

Belady现象是指内存和外存发生频繁的页面交换。