若tanα= $\frac{4}{3}$ ，则cos2α等于（  ）

班集体是我们青少年成长的摇篮和沃土，我们每个人的成长都离不开学校，更离不开班集体。为了增强同学们的群体责任感，努力为学校和班级这个群体争光，某校七年级二班在班主任的号召下，在学校做了一次调查，假如你也参加了此次调查，请你努力完成以下内容。

    Now boys and girls, I have got something to t____ you. Tomorrow is Friday. We are going to have our O____ Day. Our parents will come to school and v____ our school. They will a____ at three t____. They will s____ in the classroom and listen to our teachers. Then they will go to the p____ to see our wonderful show.

下列有关静脉血的叙述中，错误的是（    ）