标准状况下，将11.20LCl2通入到足量的石灰乳中，生成的Ca（ClO）2的质

用“220V  800W”的电炉接在220V 的家庭电路上，电炉产生热量的75% 被水吸收，在通常情况下，将一壶温度为20 ℃，质量为2kg 的水烧开，需要多长时间？

书面表达。

     根据提示写一篇70-90 词的短文，说明树木对人类的重要性，我们必须要爱护树木。

     提示：1. 树木可以美化环境（beautify the environment），有助于净化空气，有益于身心健康；

               2. 木材有许多用途，不但可用于建筑，还可用于制造许多其他的东西。

     例如，我们家中的许多东西都是木制的；3我们应种植和保护树木，严禁乱砍滥伐，以保持生态

平衡（the balance of nature）。

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所谓探亲避孕药，下述哪项是错误的：

A．探亲避孕药可在排卵期应用

B．探亲避孕药不应作为长期避孕方法

C．探亲避孕药服用时间不受周期限制

D．探亲避孕药即在必将房事时使用，无房事活动即可不用

E．探亲避孕药适合短期同居者应用

Recently divorced in my 30s, I had no job and was on my way downtown on a rainy day to go to the employment offices. I had no umbrella, for my old one had fallen apart, and I couldn’t afford another one.

I sat down in the streetcar--- there against the seat was a beautiful silk umbrella with a silver handle inlaid (镶嵌着…的) with gold and bright enamel (珐琅). I had never seen anything so lovely. I examined the handle and saw a name on it. The usual procedure would have been to turn in the umbrella to the conductor, but I decided to take it and find the owner myself.

I got off the streetcar in a downpour and carefully opened the umbrella to protect myself. Then I searched a telephone book for the name on the umbrella and found it. I called and a lady answered. Yes, she said in surprise that was her umbrella, which her parents, now dead, had given her as a birthday present, but it’d been stolen from her locker at school years before.

She was so excited that I forgot I was looking for a job and went directly to her house. She took the umbrella, her eyes filled with tears. I was only too happy to see her get back the lost umbrella, and get a job she offered me.

写作要求

以30个词概括这篇短文的主要内容。

对dBm叙述正确的是（）。

A.是相对电平单位

B.是绝对功率电平单位

C.又称“分贝毫瓦”

D.相当于10“dB”