B
考查动词。
句意:此外,还有一件简单的事最使我吃惊。
A.bored 使无聊
B.surprised 使吃惊
C.worried 使担忧
D.hurt 使受伤
根据后文Every day when the students left, they would clean up after themselves and leave their areas ____ without ever being told to do so.
每天当学生们离开时,他们会收拾干净,使他们的区域____,(虽然)没有人告诉他们这样做。可知,作者对学生们爱干净的做法还是感到很吃惊的。故选B。