HoW much are those hats?改为单数要怎么改？救你们帮帮我吧？

Answer 1

How much is the hat?
把谓语动词改为is，名词复数形式改为单数就可以了。

Answer 2

应该是：
how much are these(或者those) tomatoes?
这些（或者那些）西红柿多少钱？
改为单数句：
how much is this(或者that) tomato?
这个（或者那个）西红柿多少钱？