如果直线l1,l2相交成30°的角,交点为O,P为平面上任意一点,若作点P关于l

题型:填空题

问题:

如果直线l1,l2相交成30°的角,交点为O,P为平面上任意一点,若作点P关于l1的对称点P1是第1次,再作点P1关于l2的对称点P2是第2次,以后继续轮流作关于l1、l2的对称点.那么经过______次后,能回到点P.

考点:轴对称
题型:填空题

根据短文内容和首字母提示,填写适当的单词,使短文完整、连贯。

     The first day of April is full of fun. It is April Fool's Day. A fool on that day is a p_ 1__ who does not

think carefully and easily b    2      things that are not true.

     On April Fool's Day, people tell lies (撒谎) to fool o   3      people. They play tricks (恶作剧).

Then everyone around l     4     . You can tell a lie on April Fool's Day. If someone believes the lie, say,

"April Fool!" But you should be c    5     . Someone may tell you a lie, too. If you believe it, he or she will

say, "April Fool!"

     Here are some April Fool lies.

     "Your shoe is untied."

     "There's a bug on your shoulder (肩膀)."

     "Our teacher says we're having a math t   6       today."

     "Your bike has a flat tire (扁的轮胎)."

     You can play such an April Fool's trick:

     You n    7     a coin or a dollar bill, and the thread (线).

     Tape (用……绑起) a very long thread to the money. Put the m    8       down on the ground H    9      

the other end of the thread. Stand away.

     When someone sees the money and tries to p  10      it up, pull (拉) back the thread quickly. Laugh

and say, "April Fool!"

题型:填空题

请画出甲物体AB在平面镜中的像及完成图乙中的折射光线.

题型:填空题

绕在铁芯上的线圈L组成如图甲所示的闭合回路,在线圈的正下方放置一封闭的金属环。线圈的右侧区域分布着变化的磁场,磁感应强度B的大小按图乙所示的哪种变化,才能使金属环受到向上的吸引力 (   )

题型:填空题

两个不同的瓶子装满酒精溶液,一个瓶子中酒精浓度为75%,另一个瓶子中酒精浓度为80%,若把两瓶酒精溶液混合;则混合后的酒精浓度可能为多少( )

A.70%

B.72.5%

C.77.5%

D.80%

题型:填空题

生物耗氧量大于化学耗氧量。()

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