光污染已成为21世纪人们关注的问题。据测定，室内洁白、平滑的墙壁能将照射在墙壁上的太阳光的80%反射，长时间在这样刺眼的环境中看书学习会感到很不舒服。如果将墙壁做成凹凸不平的面，其作用之一可以使照射到墙壁上的太阳光变成散射光，达到保护视力的目的，这是利用了光的（    ）

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：在错的词下划一横线，并在该词下面写出修改后的词。

    Last Saturday afternoon, a charity sale held on our school playground. Although it was no easy task, students active participated in it.

    To organize it successfully, we' made full preparations. After the sale, from the students we collected variously second-hand goods which were still in good condition and classify them. Then came the big day. With all the teachers and students involve, the activity turned out to be successful. We raised 5,000 yuan for total at the end of the activity. All the money we raised up will go to the students from poor family to help finish their studies. It's so a meaningful activity that students look forward to the next charity sale.