题目内容：

_英语选择题要有理由______great help it is to know the customs of the country before you visit
what
what a
how
how a

优质解答

选择what a
感叹句用what、how引导,本题不缺主语、谓语,所以,help是被修饰的部分,用 what；help 不可数但这里是“有帮助的一件事”具体化了,是可数的.