问题 选择题
电气化铁路的输电线常用图所示的方式悬挂在钢缆上.钢缆的A端固定在电杆上,B端连接在滑轮组上.滑轮组由a、b、c三个滑轮构成,配重P由多个混凝土圆盘悬挂在一起组成,配重的总重为G,若不计摩擦和滑轮的重量,则以下说法中正确的是(  )

A.a为动滑轮,B端钢缆受到滑轮组的拉力大小约为3G

B.a为动滑轮,B端钢缆受到滑轮组的拉力大小约为G

C.a、c为动滑轮,B端钢缆受到滑轮组的拉力大小约为3G

D.a、c为动滑轮,B端钢缆受到滑轮组的拉力大小约为G

答案

答案:A

阅读理解

阅读理解。

     Attractive fathers do not pass their looks onto their sons but they will hand their good looks down to their

daughters, research shows.

     In a study of family photographs, Professor David Perrett and Elisabeth Cornwell-now at the University of

Colorado have found that while both father and mother can influence the attractiveness of their daughters, the

couple's good looks do not necessarily contribute to the attractiveness of their son as an adult. Handsome men

with masculine (阳刚的) looks are likely to pass on masculine features, but not facial attractiveness.

     The theory suggests it is not unusual for attractive parents to produce a beautiful daughter while failing to

pass on the same good looks to a son.

     While many celebrity mothers produce beautiful daughters-such as Goldie Hawn and her daughter Kate

Hudson or Jerry Hall and her daughter Georgia-the same is not necessarily true of celebrity fathers. Sean

Stewart, the son of Rod Stewart and his first wife Alan, would probably be judged less attractive than his model

sister Kimberly. "We can't see a strong relationship between the parents' attractiveness and the sons. If the

parents are supermodels, their daughters will be lookers," Perrett said.

     Prof Perrett said it has previously been suggested that a woman could increase her own reproductivets (繁

殖的) success by choosing a good-looking man whose genes would be passed onto male children. But the new

study, published in the current edition of the journal Animal Behaviour, disagrees with the theory.

     He said:"When we looked at women's faces, we found clear evidence that attractiveness passed from both

father and mother to daughter. For the male line, we find that facial masculinity follows the rule 'like father like

son'. Masculine dads have masculine sons. But we did not find any evidence that facial attractiveness is passed

from father to son."

1. Which of the followings is TRUE according to the passage? [ ]

A. Father and mother can influence the attractiveness of their children.

B. Handsome fathers with masculine looks will not pass on masculine features.

C. There is a strong relationship between the parents' attractiveness and the daughters.

D. If the parents are supermodels, their sons will be good-looking.

2. What does the word "lookers" in the fourth paragraph most probably mean? [ ]

A. On-lookers.

B. Models.

C. Beauties.

D. Passers-by.

3. How many celebrity families are mentioned in the passage? [ ]

A. Three.

B. One.

C. Two.

D. Four.

4. The passage is most likely to be found in a book about _____. [ ]

A. popular science

B. historical events

C. successful people

D. political systems

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