世间万物，变动不居。“明者因时而变，知者随事而制。”这说明(    )

①运动是绝对的、静止是相对的               ②一切要以时间、地点、条件为转移

③离开运动谈物质是唯心主义的观点           ④要在对立中把握统一，在统一中把握对立

增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下画一横线，并在该词下面写出修改后的词。

注意：1）处错误及其修改仅限一词；

2）只允许修改10处，多者（从第11处起）不计分。

    A good friend of me had a dog. He loved it very much that he regarded it like his best friend. Unfortunately, last Friday the dog was killed by car, which made him be heartbroken. I must did something to comfort him. To cheer him up, I went through all my old photo and made a nice picture collection of him and his dog. Hopeful, it will work. I knew I can't replace his pet and best friend but at least I can put a smile on his face again. That is how I should do for a friend. A friend in need is a friend indeed.

如图，为了测量河宽，在河的一边沿岸边选取B、C两点，在对岸岸边选择点A．测得∠B=45°，∠C=60°，BC=30米．求这条河的宽度（这里指点A到直线BC的距离）．（结果精确到1米，参考数据$\sqrt{2}$≈1.4，$\sqrt{3}$≈1.7）