.
For millions ofpeople，the American dream ofowning a home seems to be slipping out of
reach．
“Maybe young couples can no longer afford to buy a ready-made house as their parents did,'’
says 40-year-old building instmctor Pat Hennin．“But they can still have a home．Like their pioneer ancestors，they can build it themselves，and at less than half the cost of a ready-made house．”
The owner-builders came from every occupational group，although surprisingly few are professional building workers．Many take the plunge with little or no experience．“l learned how to build my house from reading books，”says John Brown，who built a six-room home for$25，000 in High Falls，New Jersey．“If you have patience and the carpentry(木匠)skill to make a bookcase，you can build a house．”An astonishing 50 percent of these owner builders hammer every nail．1ay every pipe，and wire every switch with their own hands．The rest contraet(承包)for some parts of the task．But even those who just act as contractors and finish the insides of their homes can save from 30 percent to 45 percent ofwhat a ready-made home would cost．
One survey revealed that 60 percent ofowner-builders also design their homes．Many others
buy commercial house plans for less than $100 or use plans available from the U．S． Department ofAgriculture．
49．What does the passage mainly tell us?
A．The cost of having a house built．
B．A comparison between young couples and their parents．
C．The life of owner-builders in America．
D．The American dream of owning a house．
50．It can be inferred from the passage that many Americans find it difficult to _______
A．build a house B．find aready-made house
C．have a good job D．buy a house
51．The underlined phrase“take the plunge”most probably means“_______”
A．decide to build a house B．decide to pull down a house
C．decide to buy a house D．decide to rent a house
52．From the passage we learn that_______．
A．Many house plans are offered free of charge．
B．Most of the house plans arc offered by building instructors
C．Fifty percent of the Amedcan young couples build houses．
D．Must of the owner．builders design their homes．
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时刻图线的斜率最大。将蹦极过程近似为在竖直方向的运动，弹性绳中弹力与伸长量的关系遵循胡克定律，空气阻力不计。下列说法正确的是
