(1) 의문사 + to부정사

        미래의 뜻을 나타냄. what to do, which to choose, when to begin,

        where to go 등

                ex 1) I really don't know what to say.

              = I really don't know what I should say.

           2) Do you know how to drive a car?

           3) Decide what school to go to.

   (2) too～ to = so ～ that … cannot

                ex 1) He is too old to work.

              = He is so old that he can not work.

           2) That book was too difficult for me to read.

              = That book was so difficult that I couldn't read it.

              = That was such a difficult book that I couldn't read it.

   (3) enough to = so ～ that … can ～ (～할 정도로 충분히 …하다)

              ex) Tom is strong enough to carry this box.

                = Tom is so strong that he can carry this book.