同学们做实验的装置如图所示，闭合开关，先将导体ab水平用力向右移动，导体cd也随之运动起来.则在以上的实验中下列说法正确的是（ ）

在突如其来的灾难面前，人们首先想到的是家人平安。然而，人民警察蒋敏在家中十人遇难的情况下，仍坚持抗灾第一线。蒋敏的事迹使我们认识到，当个人利益和集体利益发生矛盾时（  ）

Dear Daming，

    Thanks for your letter and the wonderful photos. I like them very much.

Here are some of my photos. I'm sending them to you . In the first photo，it is snowing. I'm making a snowman with my friends. In the second one，the sun is shining and the wind is blowing. I'm flying a kite in the park. In the third one，I'm swimming in the sea. In the last one，I am with my sister Lucy. We're playing chess.

Best wishes to you and your family.

Love，

Jack

根据书信内容选择正确答案。

赵老师是一名健步走运动的爱好者，她用手机软件记录了某个月（30天）每天健步走的步数（单位：万步），将记录结果绘制成了如图所示的统计图．在每天所走的步数这组数据中，众数和中位数分别是（  ）