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质量为m的带正电小球由空中A点无初速度自由下落，在t秒末加上竖直向上、范围足够大的匀强电场，再经过t秒小球又回到A点．不计空气阻力且小球从未落地，则（　　）

A．整个过程中小球电势能变换了mg2t2

B．整个过程中小球动量增量的大小为2mgt

C．从加电场开始到小球运动到最低点时小球动能变化了mg2t2

D．从A点到最低点小球重力势能变化了mg2t2

答案

BD

完形填空
Complete the following passage by using the words in the box． Each word can only be used once． Note that there is one word more than you need．
A． best-selling          B． influenced   C． tragic          D． canceled    
AB． in peace
AC． used to    AD． given      BC． focus   BD． comeback   C      D． concentration
A year ago, at the annual pre-Grammy party, Whitney Houston, the great diva（女歌手）, walked on stage and closed the evening with a brilliant performance．
Last Saturday, Houston was once again the  1 of the showcase before the Grammys, but her presence was a posthumous（死后的）one．
Earlier that day, pop music’s former queen was found dead in her hotel room． She was 48．
This, no doubt, is sad news to the whole music industry and her fans all over the world,   __2__ what a legendary life and remarkable career that she once had．
At her peak, Houston was the golden girl of the music world． From the mid-1980s to the late 1990s, she was one of the world’s  3 artists． She strongly impressed the audiences with effortless, powerful and peerless vocals．
Besides multi-million record sales, Houston made countless hits such as The Greatest Love of All, I Have Nothing, and the mostly famous I Will Always Love You．
She also  4 a generation of younger singers, from Christina Aguilera to Mariah Carey．
But by the end of her career, it was a  5 fall for this superstar． Houston has been addicted to drugs． Her album sales plummeted and the hits stopped coming． Her once calm and peaceful image was shattered by a wild manner and unusual public appearances, and her once natural voice became rough and hoarse, unable to hit the high notes as she  6 ．
“The biggest devil is me． I’m either my best friend or my worst enemy,” Houston told the ABC in an interview in 2002．
In 2009, Houston staged what seemed to be a successful  7 with the album I Look To You, which debuted on top of the charts．
But hoarse voice,   8 concerts, and continuous illness–Houston’s comeback trail wasn’t smooth at all． In an interview with Oprah Winfrey in 2009, Houston confessed: “It （show business） is too much． So much to try to live up to, to try to be, and I wanted out．”
Now that Houston has finally taken a break from all the chaos, may she rest  9 ．
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单项选择题

不属于宫颈癌术后并发症的是

A．感染
B．淋巴囊肿
C．尿潴留
D．心力衰竭
E．输尿管瘘
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