オリジナル問題
次の不定詞と同じ用法をもつ文を下より選びなさい。
He must be crazy to go out in this stormy weather.
選択肢1 How kind you are to say so! 
選択肢2 He isn't easy to please.
選択肢3 This river must be dangerous to
       swim in.
 
選択肢4  She was happy to read the letter.