如图,MN为⊙O的弦,∠M=50°,则∠MON等于____ .
为下列句子排序.组成一段完整通顺的对话。
(____)A.Nice to meet you too.
(____)B.Where are you from?
(____)C.Mum,this is Mike.He is my new friend.
(____)D.I am from Canada.
(____)E.Hi,Mike.Nice to meet you.
下列关于免疫对人体的主要作用的叙述不正确的是( )
— __________.