[误] It is necessary of you to do so.

[正] It is necessary for you to do so.

注：一个形容词可以用来指“行为”，又可以用来指“行为者”，如 kind, good, foolish, nice, careful, careless 这类皆是。这种形容词可以接用 of 来造句，如 It is kind of you. (行为)= You are kind. (行为者)。另外有些形容词，只能用来指“行为”，不能用来指“行为者”，如 necessary, impossible, inconvenient, unbearable 这类皆是。这种形容词是不可以接用 of 来造句的，它只能接用 for，例如 It is necessary for you to go. 而不能说 You are necessary to go.