题目

听第10段材料, 回答以下小题。 （1） What did customers use to complain about? A . Not getting through to the restaurants. B . Paying a lot for delivery. C . Slow service. （2） What is special about Door Dash? A . You can order from many places at once. B . You can check the progress of the delivery. C . The prices are lower than those from the restaurants. （3） What do we know about the work of Door Dashers? A . The hours are flexible. B . The pay isn't very good. C . It's a good way to promote themselves. （4） Why do many resta已知非零向量满足，向量a，b的夹角为120°，且||=2||，则向量，的夹角为    ．