【题目】Before Liam crossed the street, he stood watching for the traffic ________ to change.
A.signal
B.sight
C.rule
D.post

【答案】A
【解析】句意：Liam在穿过街道前，他站着等交通信号灯改变。A. signal“信号”；B. sight“视野”；C. rule“规则”；D. post“职位”。根据语境，故选A。