请教everybody,somebody,anybody的用法!

请教everybody,somebody,anybody的用法!
1.Let's begin the meeting.Is( everybody )here?
a.everybody b.somebody c.anybody
anybody任何人,无论什么人 ,是表示单数吧?又是用在否定和疑问句中的,那为什么这里却要用everybody每人,人人?
2.( Everyone )enjoys it,don't they?
a.Someone b.Nobody C.Everyone
enjoys是第三人称单数,为什么用Everyone（每人,人人）?Everyone是表示复数还是单数?Someone有人,某人,也是单数吧?为什么不能用?
3.请问以下哪些是表示单数?哪些是表示复数?哪些是用在肯定句?哪些是用在否定句和疑问句?
a.everybody b.somebody c.anybody d.everyone E.nobody f.someone G.everyone H.no one I.anyone
4.( )your friends coming to the party this evening?
a.Are b.Did c.Was
这句是现在进行时做将来时吗?
5.Mary's friends played really good( music )
a.music b.piano
Mary的朋友能弹一手好钢琴,为什么不能用piano?
6.I'm( sorry )I can't meet you today.How about next Monday?
a.shame b.sorry c.pity
为什么选择( sorry a和C都是表示遗憾,为什么不可以?
7.Did you meet (any)new people?这个(any)可加可不加吗?
8.David （arrived ）late with his friend Steve.（arrived ）改成was,句子也对吗?
9.a.We (had) a great time.我们玩的棒极了.
b.They （didn't have ）a good time.他们玩的不痛快.
当have表示“有”时,过去式是 “had”,否定形式是hadn't.；当have不表示“有”时,否定形式是didn't+动词原形.
那我搞糊涂了,A和B中的have到底是表示“有”还是不是?因为A和B,2句句子一样的have表达方式,那么为什么B不是hadn't?
10.The flat was （in ）a bit of a mess.这个（in ）是不是可加可不加?