My cousin Sandy is1English girl. Her2name is White. She is 12. The girl is3. In her room, her books and tape player4in the bookcase. Her pencil box is on the5. Her ruler is on the desk, too. And a set 6 keys are in her pencil box. A baseball is under the desk,7 it's not Sandy's. It's her brother8. Sandy has a computer. 9 on the table. There is a photo on the wall. Two girls are in the photo. Do you know10the two girls are? Well, they are Sandy's good friends, Mary and Anna.

下列哪一理论的提出，使人类对微观世界的基本认识有了革命性的进步

设一元二次方程7x²－$\sqrt{6}$x－5＝0的两个根分别是x₁、x₂，则下列等式正确的是（      ）

已知$\left\{\begin{array}{c}x=2\\ y=1\end{array}\right.$是方程组$\left\{\begin{array}{c}ax+by=5\\ bx+ay=1\end{array}\right.$的解，则a+b的值是（　　）

计算：2×（﹣3）=____．