阅读理解。
Bowing is a very important custom in Japan. Unlike people in many other countries, they greet each other
by bowing instead of shaking hands. It is impolite not to return a bow to whoever bows to you.
Bowing has many functions in one. It expresses the feeling of respect, thanks, regret, and so on. You can
bow when you say, "thank you", "sorry", "hello", "goodbye", "congratulations", "excuse me", "good morning",
and more.
Bowing seems simple, but there are different ways of bowing. Bowing techniques vary from a small nod
of the head to a long, 90-degree bow. It depends on the social position or age of the person you bow to. If
your opposite is of higher social position or older than yourself, you are supposed to bow deeper and longer
than him or her. It is polite to bow from your waist. Men usually keep their hands at their sides, and women
usually put their hands together on their legs with their fingers touching. If it is not a very formal situation,
you can bow by nodding. The most common bow is a bow of about 15 degrees.
You might feel strange doing it, but try to bow in Japan. You will be considered very polite!
1. The author writes the passage mainly to _____. [ ]
A. introduce the history of bowing in Japan
B. describe the purposes of bowing in Japan
C. introduce the Japanese custom of bowing
D. describe different ways of bowing in Japan
2. By saying "Bowing has many functions in one", the author means that _____. [ ]
A. people can express different feelings by bowing
B. one kind of bow has many similar functions
C. people bow to express their feelings
D. the more times you bow, the more respect you receive
3. How people greet in many countries? [ ]
A. by bowing
B. by shaking hands
C. by kissing each other
D. by touching
4. If an assistant wants to show respect to her professor, she may bow like _____. [ ]
A. 
B. 
C. 
D. 
，则(x0，f(x0))是曲线y=f(x)的拐点．
在某U(x0，δ)可导，因(x0，f(x0))是拐点
在x0两侧凹凸性相反
在x0两侧单调性相反
是f’(x)的极值点．对f’(x)由费马定理得f"(x0)=0．故(A)正确．
在x=x0两侧f(x)的凹凸性相反．因此，(x0，f(x0))是y=f(x)的拐点．故(B)正确．
，f’(C)=0．由f(x)是凸的
在(a，b)单调下降
在[a，c]单调上升，f(x)＞f(a)=0(x∈(a，c])，f(x)在[a，b]单调下降，f(x)＞f(b)=0(a∈[c，b))．因此，f(x)＞0(x∈(a，b))．故(C)也正确．