It is much colder in Beijing than Shanghai.修改错误The ill boy was late for school yesterday.修改错误（两题都要说明理由）

It's much colder in Beijing than (it is ) in Shanghai.
The sick boy was late for....
Sb is ill or sick.
But we can't say, an ill boy. Instead, we must say, a sick boy.
That is, an ill boy doesn't mean a sick boy.
Is ' an ill boy" an expression? Sure. it is. But it means " a bad or ill- willed boy".

much改成more，从colder得知这里要用比较级，much的比较级是more，与than构成固定搭配more than.
ill改成sick（ill只能做表语，表语是用在be动词和系动词后的，不可以用在名词前面，而sick既可以作表语也可以作定语）
不明白可以问我。

It is much colder in Beijing than in Shanghai.比较不一致
The sick boy was late for school yesterday.ill只能做表语,不能做定语