问题 选择题

功率为l0W的发光二极管(LED灯)的亮度与功率为60W的白炽灯相当。根据国家节能战略,2016年前普通自织灯应被淘汰。假设每户家庭有2只60W的白炽灯,均用10W的LED灯替代,估算出全国一年节省的电能最接近(   )

A.8×l08 kW.h

B.8×l0l0 kW.h

C.8×l0ll kW.h

D.8×l013 kW.h

答案

答案:B

题目分析:每户家庭功率节省100W,中国人口约为13亿,大概4亿户家庭,每天开灯5小时,则一年全国节省的电能为,故选B

点评:本题难度较小,电功率指的是1s时间内消耗的电能,kwh这个单位是电功的单位,不是电功率,要理解并能应用该单位解题是关键

多项选择题
单项选择题

(A)

Linda Evans was my best friend—like the sister I never had. We did everything together: piano lessons, movies, swimming, and horseback riding.

When I was 13, my family moved away. Linda and I kept in touch through letters, and we saw each other on special time—like my wedding and Linda’s. Soon we were busy with children and moving to new homes, and we wrote less often. One day a card that I sent came back, stamped "Address Unknown." I had no idea how to find Linda.

Over the years, I missed Linda very much. I wanted to share happiness of my children and then grandchildren. And I needed to share my sadness when my brother and then mother died. There was an empty place in my heart that only a friend like Linda could fill.

One day I was reading a newspaper when I noticed a photo of a young woman who looked very much like Linda and whose last name was Wagman—Linda’s married name. "There must be thousands of Wagmans," I thought, but I still wrote to her.

She called as soon as she got my letter. "Mrs. Tobin!" she said excitedly, "Linda Evans Wagman is my mother."

Minutes later I heard a voice that I knew very much, even after 40 years, laughed and cried and caught up on each other’s lives. Now the empty place in my heart is filled. And there’s one thing that Linda and I know for sure: We won’t lose each other again!

There was an empty place in the writer’s heart because she()

A.was in trouble

B.didn’t know Linda’s address

C.received the card that she sent

D.didn’t have a friend like Linda to share her happiness or sadness