$\frac{1}{9}$的算术平方根是____

在水温和搅拌条件相同的情况下，我们可以通过____加快水果糖的溶解。

    It's Sunday morning. The students of Class 3 are giving their classroom a good cleaning. Miss Huang, their teacher, is working with them. The children are busy. Some are carrying water, some are cleaning the windows, others are sweeping the floor. Zhang Hua is putting up a map on the wall. It is a map of China. Wang Fei and Wei Qing are mending some broken chairs. The children are listening to the radio while they are working. The classroom looks nice and bright after the cleaning. The children are very happy. They go home for lunch at noon.

如图，在平面直角坐标系中，正方形OABC的边长为4，顶点A、C分别在x轴、y轴的正半轴，抛物线y=﹣$\frac{1}{2}$x²+bx+c经过B、C两点，点D为抛物线的顶点，连接AC、BD、CD．