Which of the followings is a valid Scheme form?

Which of the followings is a valid Scheme form?

Which of the followings is a valid Scheme form?

    Answers:

    A.
    (* 9 (/ (- 4 2) 7))
   
    B.
    * 9 (/ (- 4 2) 7)
   
    C.
    *9 / - 4 2 7
   
    D.

    9 * (4 - 2)/7

Answer. A.