1 . 双星是两颗星，是由相互围绕旋转的两颗星组成。
A binary star is a double star, __________ two stars turning round each other.

2 . Nanjing is no longer what it was. Great changes _____ in the past few years.

A．were taken place	B．are taken place
C．have taken place	D．are taking place

3 . It ________ that after the ash covered the people who failed to flee the city, their bodies nearly completely broke down and disappeared, ________ empty spaces in the ash.

A．is turned out; left	B．is turned out; left
C．turns out; leaving	D．turns out; left

4 . The rapid economic growth that _____ in China in recent years has resulted in great improvements in living conditions for many Chinese.

A．took place

B．has taken place

C．has been taken place

D．was taken place

5 . Microsoft ended support for Windows XP after April 8, which _______a major operating system for some Chinese computer users, and advised users to upgrade to Windows 8.1.

A．remained

B．remains

C．is remaining

D．is remained