下列与金属有关的说法正确的是( ) A．生铁和钢都是铁的合金 B．废旧电池可以随

汽车在平直的公路上以20m／s的速度行驶，当汽车以5m／s²的加速度刹车时，刹车2s内与刹车6s内的位移之比为

A．1：l

B．4：3

C．3：l

D．3：4

A、B两种微藻对磷元素需求较高，用相同的培养液分别培养A和B得到两种微藻的生长曲线如图甲所示，图乙表示A、B微藻在不同浓度的磷元素下的生长速率曲线。现将两种等体积的微藻混合培养在磷元素浓度为X的环境中，若只考虑磷浓度的影响，那么随时间的推移预期两种微藻的数量变化曲线可能是

A．

B．

C．

D．

There are over one million superstitions(迷信), and most people believe at least one or two of　them.

Many people are superstitious about numbers. They think that there are lucky numbers and unlucky numbers.

The number 13 is often considered unlucky. In some parts of the world, buildings have no 13th floor and streets have no houses with the number 13. In Japan, "4" is considered unlucky because in Japanese the word "four" is pronounced the same as the word "death" .

Japanese never give gifts of four knives, four napkins, or four of anything.

What are the lucky numbers? Seven is a lucky number in many places, and "8" is considered a lucky number in Japan and China. In China, businesses often open on August 8, and many couples register to get married at eight past eight on August 8.

Superstitions about numbers are so widespread that some people--called numerologist--make a living by giving advice about numbers.

In 1937, when the Toyoda family of Japan wanted to form a car company, they asked a numerologist if "Toyoda" would be a good name for the company. The numerologist said it would not be. He explained that "Toyota" would be a better name for the company. The family took his advice. As a result, millions of people drive "Toyota" and not "Toyoda" .

There are many other kinds of superstitions. There are superstitions about eating, sleeping, sneezing and itching(抓痒). There are superstitions about animals and holidays and horseshoes.

There are even superstitions about superstitions. Those superstitions will tell people how to reverse bad luck.

When the Japanese bump heads, they immediately bump heads again. According to a Japanese superstition, the first-bump means their parents will die, but the second bump "erases" the first bump         

To reverse bad luck in general, people turn around three times, turn their pockets inside out, or put their hats on backwards.

In the United States, baseball players sometimes wear their caps backwards when their team is losing. It looks silly, but the baseball players do not mind if it helps them win the game.   

小题1:It can be inferred that superstitions about numbers are           .

A．popular neither in Japan nor in China

B．popular only in Japan and in China

C．popular both in Japan and in China

D．causing great troubles both in Japan and in China小题2:The underlined word " reverse " means           .

A．change to bad luck

B．cause to go in the opposite direction

C．change for the worse

D．exchange小题3:If a Japanese purposely bumps his head again after an accidental bump, we can be sure that     .  

A．he is mad

B．he is happy

C．he is superstitious

D．he is very sad小题4:The writer wrote this passage with the purpose of           .

A．persuading us to believe superstitions

B．showing us some facts of superstitions

C．showing us the magic power of number

D．showing us a numerologist

加强钻井液中固相的清除，使密度（）。

A、增加

B、降低

C、不变

D、无法判断

数学大观本课程强调的是（）。

A、技巧

B、方法

C、思想

D、文化