如图所示，自动卸货车静止在水平地面上，车厢在液压机的作用下，_爱下问搜题

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问题选择题

如图所示，自动卸货车静止在水平地面上，车厢在液压机的作用下，θ角缓慢增大，在货物相对车厢仍然静止的过程中，下列说法正确的是（）

A．货物受到的支持力变小

B．货物受到的摩擦力变小

C．货物受到的支持力对货物做负功

D．货物受到的摩擦力对货物做负功

答案

答案：A

题目分析：货物受重力、支持力、摩擦力的作用，根据平衡条件得，，θ角缓慢增大的过程中，支持力变小，摩擦力增大，所以A正确；B错误；根据做功的公式知，支持力做正功，故C错误；摩擦力不做功，所以D错误。

阅读理解

阅读理解。

To: "The Shoe People" inquiries@shoepeople.com
From: "John Trimbald" jtconstruction@img.com <>
To Whom it May Concern,
I have trusted the Shoe People to protect the feet of my employees for over ten years now. I
recently purchased a few pairs of boots from your company for my crew. Though my men were
initially satisfied with the boots, the soles(鞋底) began to fall apart on them after just twelve weeks.
This was extremely surprising considering they came with a six year warranty(担保). The boots are
unsafe to wear because my men are pouring hot concrete. Please respond as soon as possible with
instructions on how I can return the boots and receive a refund.
Thank you, John Trimbald, Foreman, JT Construction

To: John Trimbald" jtconstruction@img.com
From: "The Shoe People" <inquiries@shoepeople.com>"
Dear Mr. Trimbald,
     Thank you for your e-mail concerning the poor quality of our rubber soled black workboots.
A representative will be by your office next week to pick up the damaged boots. We apologize for
any inconvenience this has caused you and your crew.  Along with five new pairs of workboots for
your crew (we included one extra pair), we have enclosed a free year's supply of spray(喷雾). In
our retail stores, this spray is always recommended to buyers who work on heated floors. This should
have been brought to your attention at the time of your initial order (received by telephone on
October 12, 2007). Please excuse our oversight. To date we have had no complaints about these
workboots from customers who have used the protector spray. However, should you use the spray
and find that you are still unsatisfied with the boots, please return the boots and spray for a full refund.
     Thank you for supporting The Shoe People. Have a Happy New Year.  Sincerely, Stan Mason,
President

1. The first email is basically an email of __________.

A. apology
B. sympathy
C. appreciation
D. complaint

2. What is the "spray" used for according to the passage?

A. To repair the damaged boots.
B. To protect the soles from heat.
C. To prevent the crew from danger.
D. To protect the boots from concrete.

3. According to the president of The Shoe People, John Trimbald ________.

A. can exchange the damaged boots with new ones at any time
B. must return the damaged boots to any of the retail stores
C. will get new pairs of boots and a free year's supply of spray
D. can return the damaged boots and spray for a full refund now

判断题

神经元是神经系统基本的结构和机能单位。