题干

据《化学世界》期刊介绍,我国著名化学家徐辉碧教授根据众多实验事实,提出硒(元素符号Se)与艾滋病的发生和发展有关。硒的一种化合物K2SeO4中硒元素的化合价为____价。已知K2SO4的名称为硫酸钾,则K2SeO4的名称为____

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+6,硒酸钾

同类题2

阅读短文,完成练习。

    战国时魏国有一个有名的射箭能手叫更羸。

    有一天,更羸跟随魏王到郊外去游玩。玩着玩着看见天上有一群鸟从他们头上飞过,在这群鸟的后面,有一只鸟吃力地在追赶着它的同伴,也向这边飞来。更羸对魏王说:“大王,我可以不用箭,只要把弓拉一下,就能把天上飞着的鸟射下来。”“会有这样的事?”魏王不相信地问。更羸说道:“可以试一试。”过了一会儿,那只掉了队的鸟飞过来了,它飞的速度比前面几只鸟要慢得多,飞的高度也要低一些。这只鸟飞近了——原来是只掉了队的大雁,只见更羸这时用左手托着弓,用右手拉着弦,弦上也不搭箭。他面对着这只正飞着的大雁拉满了弓。只听得“当”的一声响,那只掉了队正飞着的大雁便应声从半空中掉了下来。

    魏王看到后大吃一惊,连声说:“真有这样的事情!”便问更羸不用箭凭什么将空中飞着的鸟射下来的。更羸笑着对魏王讲:“没什么,这是一只受过箭伤的大雁。”“你是怎么知道这只大雁是受过了箭伤的呢?”魏王更加奇怪了。更羸笑着对魏王说:“从这只大雁飞行的姿势和叫的声音中知道的。”更羸接着讲:“这只大雁飞得慢是它身上的箭伤在作痛,叫的声音很悲惨是因为它离开同伴已很久了。旧的伤口在作痛,还没有好,它心里很害怕。当听到弓弦声响后,更害怕再次被箭射中,于是就拼命往高处飞。它心里本来就害怕,加上拼命一使劲,未愈的伤口又裂开了,疼痛难忍,翅膀再也飞不动了,它就从空中掉了下来。”

 (选自《中国古代寓言故事》)

同类题4

阅读理解

    Maybe you are aware that the latest job markets news isn't promising: Unemployment is still more than 9 percent, and new job growth has fallen close to zero, which is bad for economy, of course. And it may be especially discouraging if you happen to be looking for a job or hoping to change careers right now. But it actually shouldn't matter to you nearly as much as you think.

    That's because job growth numbers don't matter to job hunters as much as job turnover data. After all, existing jobs open up every day due to promotions, resignations, terminations, and retirements. In both good times and bad, turnover creates more openings than economic growth does. Even in June of 2007, when the economy was still falling along, job growth was only 132,000, while turnover was 4.7 million!

    And as it turns out, even today — with job growth near zero — over 4 million job hunters are being hired every month.

    I don't mean to imply that overall job growth doesn't have an impact on one's ability to land a job. It's true that if total employment were higher, it would mean more jobs for all of us to choose from. And it's true that there are currently more people applying for each available job opening, regardless of whether it's a new one or not.

    But what often distinguishes those who land jobs from those who don't is their ability to stay motivated. They're willing to do the hard work of identifying their valuable skills; be creative about where and how to look; learn how to present themselves to potential employers; and keep going, even after repeated rejections. The Bureau of Labor Statistics data showed that 2.7 million people who wanted and were available for work hadn't looked for a job within the last four weeks and were no longer even classified as unemployed.

    So don't let the headlines fool you into giving up. Four million people get hired every month in the U.S. You can be one of them.