【間違いやすい英語 17】I'm afraid of say this

(こんなことを言ってすみませんが)はどこが不自然でしょうか。

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A) I'm afraid to say this.

(afraid to [動詞の原形] 、　afraid of [動名詞～ing］saying)

I'm happy of help you.

I'm happy to help you.

I'm sorry of inform you.

I'm sorry to inform you.