Hello, I'm Jack. I live in a house. My address is 246 Second Street. It's far from the school. So I go to school by bus every day. But my house is near the park. So I often go to the park on foot. Tom is my friend. He lives in a house, too. It is near the school. So he goes to school on foot every day.

已知$\sin 2\alpha =\frac{1}{3}$，则${\cos }^2\left(\alpha -\frac{\pi }{4}\right)=$（   ）

某同学拟选择一种半透性的膜材料,用于自制渗透计。他采用如图1所示的装置(示意图)，对收集到的四种材料甲、乙、丙和丁进行试验，得到了倒置漏斗中的液面高度随时间变化的曲线(如图2)。据图分析，该同学应选择的膜材料是(    )

一块菜地的形状如下图所示，它的面积是____ $m^2$ ．