This is a wonderful garden.改为感叹句.

What a wonderful garden it is!
How wonderful the garden is!

what a wonderful garden
How wonderful the garden is

How wonderful the garden is.
What a wonderful garden it is.

What a wonderful garden it is！
How wonderful the garden is！

what a wonderful garden ！
How wonderful the garden is！

How +形容词+主语(名词)+谓语
How wonderful the garden is.

what +名词(这个名词是被某个形容词修饰的) (+主+谓)
what a wonderful garden (it is).