be useful to是加do还是加ing?

Question

如题所述

Answer 1

sth be useful to sb某事对于某人是有用的
it is useful for sb to do sth 对于某人来说做某事是有用的（to do 是主语）
例如:This book is useful to you
It is useful for you to read this book
.

Answer 2

be useful to sb 或者 be useful to do sth本回答被提问者采纳

Answer 3

be useful to do sth
be useful to sb
be useful for sth/doing sth

参考资料：牛津高阶

Answer 4

doing