I find it hard to concentrate on studying with the radio ______.
(A) turning on
(B) on
(C) be turned on
(D) to turn on
答案為B 為什麼A不行呢

on off 本身就有開關意味， 這邊若強調動作turn要使用過去分詞turned on才對on (廣播是被開的)