Restaurants must stop offering free plastic bags in Beijing _______ customers ask for them.
句意：北京的餐厅必须停止提供免费塑料袋，除非顾客要求。
考查连词辨析。since自从；unless除非；because因为。根据Restaurants must stop offering free plastic bags in Beijing及customers ask for them，可知，除非顾客主动要，否则北京的餐厅不可以提供免费塑料袋，后文表条件，所以空格处填引导条件状语从句的连词unless。故选B。
Restaurants must stop offering free plastic bags in Beijing _______ customers ask for them.
—Tim, our foreign teacher Ms. Green will go back to England next week.
—Really? Let's have a party to say goodbye to her ______ she is free this weekend.
______ you keep moving, you'll never reach the top of the mountain.
—Do you know the traffic rules?
—Sure, one of them is that we can’t go across the street _____ the light is green.
I waited ______ they finished talking.
Get up early, ______ you will miss your train.
Nobody can hear you ______you speak in a louder voice.
—I think I am the shyest in my class. What should I do?
—Be more active in class, ________ you can improve your ability to express yourself.
—Mary doesn’t like fish chicken
—Ben doesn’t like fish, he likes chicken very much.
The Chinese doctors went to Italy to help the patients________they knew it was dangerous.
