Here is the bulletin board of Class 3. Some of the students put their notes on it. Please read them and answer the following questions.

小题1:The Chinese meaning of "bulletin board" is _______.

A．电影广告

B．寻人启事

C．公告栏

D．通缉令小题2:According to the notes on the bulletin board, what holiday might be coming?

A．Christmas

B．Halloween

C．Thanksgiving

D．New Year's Day小题3:When Julia is busy, what does Alex always help her do?

A．To do math homework.

B．To clean the windows.

C．To have P. E. class together.

D．To take books to school.小题4:From the bulletin board, we know that Mr Chen is a ___________.

A．repeater

B．P.E. teacher

C．doctor

D．pilot小题5:Why does Bill lend books to Mario?

A．They are classmates.

B．Miss Li wants him to do so.

C．Bill has too many books.

D．Mario forgot to bring his books to school.

在潮流界以上河段内的水流，流向虽总是顺流而下的，由于还受到潮流的顶托作用，水位还有周期性升降变化，这种水位变化越向上游越不显著，到完全不受潮波影响处称为()。

A.潮区界 

B.潮流界 

C.混合点 

D.海水与淡水混合区