可数名词

apple

It's such a beautiful butterfly!多漂亮的蝴蝶阿
They're such losers!他们真是衰人

Do you have any other book to read?
I often cook my mother her favorite food.
It sounds good to me.
It sounds like you are playing a music with piano.
I ofter write to Lily.
The store is on her right.
The library is on my left.

1和4

可数有单数和复数两种形式.指一个人或一件事物时,用单数形式；指两个或多个人或事物时用复数形式.名词由单数形式变成复数形式的规则如下：
一般的名词词尾直接加-s .如：
book → books room → roomshouse → houses day → days
以s,　ss, ch,　sh, x 结尾的名词,在词尾加-es .如：bus → buses glass → glasseswatch → watchesdish → dishes box → boxes
以"辅音字母+y"结尾的名词,要先将y改为i再加-es.如：city → cities body → bodiesfactory → factories
以f 或fe 结尾的名词,要将f或fe改为v再加-es.如：half → halves leaf → leavesknife → knives wife → wives
特例 [悄悄话：特例常常考,要记住.
① child → children
② man → men woman → womenpoliceman → policemen(规律：man → men)③ tomato → tomatoespotato → potatoes[悄悄话： 初中英语以o 结尾的名词变复数时只有这两个词加-es,其余的当然加-s喽!如：photo → photos ]
④ foot → feet tooth → teeth[悄悄话： oo变成ee.]
⑤ sheep, Chinese, Japanese单、复数同形　[悄悄话：变复数时词形不变.
⑥ people单数形式表示复数意义,要求谓语动词用复数；　people的复数形式peoples通常指“多个民族”.

man,river,book,glass,desk,cup,road,car,eye,foot,tree,bird,girl,boy.

other作定语时后面既可以接名词复数又可以接名词单数。

noise 通常情况下指噪音,这时是不可数名词.
当 noise 泛指声音、声响时,为可数名词.

一般都是复数

不定冠词用a还是用an主要是由后面的词来决定的!虽然原句中的不定冠词修饰的是中心名词sister,但是由于sister前面的定语,elder是由元音音节开头的,注意不是以元音字节母开头的,所以就应用an