这些英语句子错在哪里？

1.Mike is a English boy.
a→an English开头字母是元音的，得用an

2.Mr Jiang is not an Chinese teacher.
an→a 句中的Chinese开头字母是辅音的，用a

3.Spell"key",please.---Yes,K-E-Y
key前加the ,特指这个单词

4.What's that for Chinese?
for→in 用汉语怎么说应该是in

Mike is an English boy
Mr Jiang is not a Chinese teacher
Spell"key",please.---K-E-Y
What's that in Chinese

Mike is an English boy.
Mr jiang is not a Chinese teacher.
Spell "key" please. Ok, KEY
What's that in Chinese?

这几个这么短的句子找错，不知道是不是这样的改法，如果另有深意，很期待高人指点。

Mike is an English boy.
Mr. Jiang is not a Chinese teacher.
Spell the "key",please.---Yes,K-E-Y
What's that in Chinese？