水处理装置一般按净化程度分成三级。二级处理关于BOD5的净化率为（)。A．25%~40%B．45%~90%C．90%左右D

A．He didn't know that David was having a problem.

B．The woman doesn't know much about accounting.

C．David hasn't started working on his project yet.

D．David is going to ask the woman for help.

Not until Dr. Brown came to the city ______ what kind of the city she is.

A．did he know B．he didn't know

C．he knew D．he could know

Not until Dr. Brown came to the city ______ what kind of the city she is.

A．did he know B．he didn't know

C．he knew D．he could know

听力原文：W: Do you know？ Henry didn't win that speech contest.

M: Didn't he？ I thought for sure he would. He worked so hard on it.

W: Maybe that's why he lost. They thought he was simply reciting.

How does the man feel about the result？

A．He thinks it is unbelievable.

B．He thinks it was too hard for Henry.

C．He thinks Henry worked too hard.

D．He thinks Henry was not given a chance.

Why does the man know so much about San Francisco？

[A] He thinks the city is pretty.

[B] He likes to talk with people.

[C] He travels a lot in the city.

[D] He teaches ethnic history at a university.

Little______that the police are about to arrest him.

A．does he know

B．he knows

C．he doesn't know

D．he didn't know

A、he read too much about plane crashes and tried to avoid flying unconsciously

B、he wanted to take a private plane instead of a public one

C、he didn't know air travel is safer than highway travel

D、he knew he was reluctant to fly but was unable to do anything about it

A．fix

B．to fix

C．fixing

D．fixed