如图所示，要想在光屏上出现缩小的像，应该把点燃的蜡烛放在（　　）

木工师傅用刨子可将木板刨平，如图，经过刨平的木板上的两个点，就能弹出一条笔直的墨线，而且只能弹出一条墨线，用数学知识解释其道理正确的是（　　）

已知直线l₁： 和直线l₂： .①当____时， 与 相交于一点；②当____时， ，此时方程组 的解的情况是____；③当____时， 与 重合，此时方程组 的解的情况是____.

A

Welcome to Happy Winter Camp

    The 2017 Happy Winter Camp is between 8:30 a.m. and 11:00 a.m.  from  February 1^st to February 8^th. All kids aged 12 to 16 are welcome. Each kid can join in only one of these activities and needs to pay￥200 for it.

⒈Music clubs (singing, piano, violin, guitar, etc)

⒉Art clubs (drawing, painting, photo-editing, etc)

⒊Sports clubs (baseball, basketball, soccer, volleyball, skiing, etc)

⒋Language Center (English, Japanese, French, etc)

   If you really want to have an interesting winter holiday, please join us. You can come to our hotel to book your seat. Also you can phone or email us.

Add: Hongxing Hotel, No. 528, Zhongshan Street, Hangzhou Tel: 0571-83033698

E-mail: camping2017@sina.com

已知A、B、C、D、E都是周期表中前四周期的元素,且原子序数依次增大,其中A原子核外有三个未成对电子;A与B可形成离子化合物B₃A₂;C元素是地壳中含量最高的金属元素;D原子核外的M层中有两对成对电子;E原子核外最外层只有1个电子,其余各层电子均充满。请根据以上信息,回答下列问题(答题时,A、B、C、D、E用所对应的元素符号表示):