题目

parent,  tell, call, celebrate, together, why,  start,  after,  shop,  newspaper    Most people buy lots of presents just before Christmas. But some people think we buy too much. They start a special day   1   Buy Nothing Day. They don’t want anyone to go   2   on that day. Buy Nothing Day is on November 29. It is   3   Thanksgiving. Often, before Christmas we see many ads. in   4   and on TV   5   us to“buy, buy, buy!”The idea for Buy Nothing Day   6   in Vancouver, Canada. Now people all over the world   7   Buy Nothing Day. In California, th给出如下四个命题①对于任意的实数α和β，等式cos（α+β）=cosαcosβ-sinαsinβ恒成立；②存在实数α，β，使等式cos（α+β）=cosαcosβ+sinαsinβ能成立；③公式tan（α+β）=成立的条件是α≠kπ+（k∈Z）且β≠kπ+（k∈Z）；④不存在无穷多个α和β，使sin（α-β）=sinαcosβ-cosαsinβ；其中假命题是A.①②B.②③C.③④D.②③④