It is true that light travels in a straight line and never -- it hits something that reflects it
问题描述：
It is true that light travels in a straight line and never -- it hits something that reflects it
A.turns until B.bends unless C.breaks when D.changes until
答
从单词意思去考虑
turn 转弯,改变方向（很多意思,根据题意取这个）
bend 弯曲,弯腰
break 破坏
change 改变
所以B和C可以直接排除,A和D比起来,A的意思更明确,就是（光的）方向改变,更符合题意