—How time flies! The middle school life is coming to an end.
—Yes. We have to say goodbye, ________ our friendship will last forever.
句意：——时间过得真快啊！中学生活即将结束。——是的。我们不得不说再见，但我们的友谊会天长地久。
考查连词辨析。and和；but但是；or否则。空前句意“我们不得不说再见”，空后句意“我的的友谊会天长地久”，句意出现转折，用but表转折。故选B。
—How time flies! The middle school life is coming to an end.
—Yes. We have to say goodbye, ________ our friendship will last forever.
Mike and Jim's room is tidy, ______ their sister's not.
Our English teacher is nice and patient she is very strict with us.
Even if we learn something well, we will forget it ______ we use it.
Wash your hands before meals, ______ you may get ill.
—Who went to the graduation party last night, Mary?
—Almost everyone did. ______ lots of students _____ Ms. Wang appeared at the party.
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.
