在水平桌面上有一个盛有水的容器，木块用细线系住没入水中，如图甲所示，将细线剪断，木块最终漂浮在水面上，且有$\frac{2}{5}$的体积露出水面，如图乙所示。下列说法正确的是（　　）

下面有关自由组合定律的叙述，正确的是：

阅读下面的语言材料，从下面每小题的A、B、C、D四个选项中选出最佳选项。

      My name is Jenny. I have been volunteering for about 16 years. I got a serious illness so I had to stop working. My sister suggested that I should do voluntary work which I had never thought of before.

      I then decided to start volunteering in a hospital. The volunteers were making a team and chatting and I thought I'd like to help patients in that way too. In the Chapel (小礼拜堂), we take it in turns to do prayers (祈祷) for patients and we each have a room where we go and talk to patients. In the hospital, I often make tea and speak to patients especially if I see the patients who are sitting there on their own or don't have visitors. I go to the Chapel every Wednesday afternoon and go to work in the hospital on the second Monday in a month.

     There are so many good things about volunteering — meeting a lot of new people and building a friendship with them. I get as much as the patients do. I feel useful now and it's terrific to think I am making a difference to somebody. Some people are looking forward to seeing you the next week. Volunteering is the best thing I've ever done.

设复数z₁，z₂在复平面内的对应点关于虚轴对称，z₁=2+i，则z₁z₂=（   ）

画○，○比□多2个。

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