问题补充：
A high-tech exhibition in the National Museum now. Let’s go and visit it.
A. will be held
B. is being held
C. was held
D. has been held
答案：
A. will be held
(答案→)B. is being held
C. was held
D. has been held
解析：考查时态语态：句意：一个高科技展览在国家博物馆举行。我们去看看。时间是now，A high-tech exhibition和hold的被动关系，用现在进行时的被动，am，is，are+being done。选B。
