難易/安全・危険/快・不快 を表す形容詞 →It is ~ to doのみ使用可能 ・The problem is easy to solve.「問題を解決するのは簡単だ」 = It is easy to solve the problem. * It is easy that you solve the problem.
・He is very sick and the doctor recommended that he not go to work for another two weeks. 「彼は重病で、医師はあと2週間は仕事に出ないようにと勧めている」⇒shouldの省略と考える:should not goも可能