题目
已知某物体做直线运动，在前一半时间内的平均速度是v1，后一半时间内的平均速度是v2，全程的平均速度是v，且v=2v1，则v1与v2的比值是（ ）A. 1:3 B. 3:1 C. 1:1 D. 1:2 答案：【答案】A【解析】先根据平均速度的公式分别求出两段时间的位移，则全程的平均速度等于两段总位移除以总时间。运动的总时间为2t，前一半时间运动的路程，后一半时间运动的路程，则全程的平均速度v，由于v，即2，即3，即。33、HOW AMERICANS LIVE
Single parents living
With at least one child
Married couples
Without children
New York
is America’s largest
city, however, it may also be the country’s loneliest
city. People living alone make up forty-eight percent of all households(家庭) on the island of Manhattan.
“I think it’s
the best way to live,” James Conaboy, a 35-year-old New
York musician said, “If you want to make a mess, you
can make a mess. If you want to paint the walls a certain color, you can do it
. “
In the USA, there are
more single-person households than classic nuclear families----a married couple
and their natural children----according to a latest report. Other cities with
high percentages(百分比) of
single households are Washington DC, St. Louis, Denver and San Francisco.
The high number of
single households shows today’s values. People living alone, especially unmarried women used to
have something to do with sadness. That feeling is no longer true. Self-esteem（自尊）isn’t based on having children and being
married any more.
1. New York may be the loneliest
city of the USA because_______
A. many people often feel lonely.
B. most of the people there often
live alone.
C. there are nearly half of
single-person households.
D. people can do what they like by
themselves.
2.What does the underlined word it
refer to (指的是)？
A.
Painting the walls. B. Making a mess.
C. Living
alone. D. Being married.
3. Which of the following can best
explain the chart(图表) on
the left of the text ?
A. There
are more single-person households than classic unclear families.
B. The
high number of single households shows today’s values,
C. People
living alone make up 48% of all households in the world.
D.
Unmarried women used to have something to do with sadness
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