已知圆M：（x-2）²+（y-3）²=1与圆N：x²+y²+2x+2ay+a²-15=0外切，则a=______．

根据汉语提示，写出下列句子空白处各单词的适当形式。每空限填一词。

Should friends be the same or different?  I don’t really  小题1: (在意). As a   小题2:   (谚语) goes, “True friends should help to bring out the best in each other .” I like sports and I always play sports. But my best friend Mike only exercises     小题3:   ( 两次) a week. So you see I’m stronger     小题4: ( 比) him. He likes reading. And he works really hard. His 小题5:   (成绩) are better. He 小题6:    (尽力) to help me with my lessons.      小题7:   (或许) I should help him make his body stronger. We    小题8: (两者都) enjoy Wang Feng’s      小题9:  (歌). We can      小题10:  (分享 ) everything.