给下列加下划线的字注音或根据拼音写汉字。

“适度的悲伤可以表示情感的深切，过度的伤心却证明智慧的短缺。”这句话告诉我们（    ）

A

    There used to be many beautiful flowers in our garden. Among them was a beautiful blue flower. My husband once told me that it only bloomed (开花) in spring and the sun in summer was too hot for it. When summer came, he would move it out of the garden and put it inside our house.

    Once, my husband was away for some time on business, so I had to take care of the flowers. Before leaving, he told me to pay special attention to the blue flower. I planned to look after it as my husband had ever done, but I was too busy to remember it. One weekend when I wanted to move the blue flower into the house, I found that it had already died. I was very sad and regretted not taking good care of it earlier.

    A week ago, my husband's elder sister, Linda, died of serious stomach cancer. Linda was much older than my husband. Maybe because of the age distance, we were not very close. After she died, we were very sad and regretted not visiting her often.

    Linda's death reminds me of the blue flower. We should have done something better, but we haven't tried our best. I believe that God has given us enough time to plant some wonderful things that will bloom inside us, but we have missed it.

如图，正方形ABCD的边长为2cm，△PMN是直角一块三角板（∠N=30°），PM＞2cm，PM与BC均在直线l上，开始时M点与B点重合，将三角板向右平行移动，直至M点与C点重合为止．设BM=xcm，三角板与正方形重叠部分的面积外ycm²．

下列结论：

①当0≤x≤$\frac{2}{3}\sqrt{3}$时，y与x之间的函数关系式为y=$\frac{\sqrt{3}}{2}$x；

②当$\frac{2}{3}\sqrt{3}$≤x≤2时，y与x之间的函数关系式为y=2x﹣$\frac{2}{3}\sqrt{3}$；

③当MN经过AB的中点时，y=$\frac{1}{2}\sqrt{3}$（cm²）；

④存在x的值，使y=$\frac{1}{2}$S_{正方形ABCD}（$\frac{1}{2}$S_{正方形ABCD}表示正方形ABCD的面积）．

其中正确的是 ____（写出所有正确结论的序号）．