若α∈（$\frac{\mathrm{\pi }}{2}$，π），则3cos2α=sin（$\frac{\mathrm{\pi }}{4}$﹣α），则sin2α的值为（　　）

如图所示，将重为5N的木块放入烧杯中，静止时木块所受浮力的大小为____ N，放入木块后，烧杯底部所受水的压强比原来____（填“变大”、“变小”或“不变”）．

抗甲型H1N1流感的有效药物“达菲”可用莽草酸（化学式C₇H₁₀O₅）制取．有关莽草酸的说法中正确是（　　）

    We eat food with the help of hands every day. It is possible for some germs(细菌) to get into our bodies. So it is important to know how to wash hands in the right way.

    A piece of news from CCTV says that students from Guangzhou have a good way of learning how to wash hands. They learn it through doing hands-washing exercises during the ①break. The teachers there say most students wouldn't like to listen but they like to act. So now the students are interested in the interesting exercises. They are learning carefully. ②They want to be teachers for their parents and friends after they learn them well.