锌对青少年儿童身体发育有重大作用，为了补锌应多食用的食品种类是（）

增加：在缺词处加一个漏词符号(/\)，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）每处错误及其修改均仅限一词;

2）只允许修改10处，多者(从第11处起) 不计分。

    As the saying goes, many little drop of water make an ocean. A small action may lead to major changes took place in society. My friends and I had participated in a voluntary activity at a nursing home last week. We first did some cleaning or washing. After that we spent half an hour chatted with the old people living there. Though it was a tired day, we were happy with that we did. I felt a sense of responsibility by visiting the old. If all of us lend a helping hand to the people in need, they can live in harmony with each other. A society is just as a family. If we are willing to help others, our small actions can make big difference.

蚯蚓是森林中的土壤动物之一，主要以植物的枯枝败叶为食．为探究蚯蚓对森林凋落物的作用，研究者做了如下实验．

（1）研究者选择4个树种的叶片做了不同处理，于6～9月进行了室外实验．每种叶片置于两个盆中（未分解叶与半分解叶），与土壤混合均匀，将数目相等的蚯蚓置于其中饲养，统计蚯蚓的食物消耗量，结果如下表．单位体重蚯蚓日平均食物消耗量（mg/（g．d））

①为了排除土壤中原有动物和微生物对实验的影响，应该在实验前对土壤进行____ 处理．

②据表分析，蚯蚓对半分解叶的消耗量明显____ （填“高于”或者“低于”）未分解叶的消耗量．

（2）用样方法调查白桦植物的种群密度时，为尽量减少实验误差，保证数据的科学性，应注意做到____ 并计算平均值．从生态系统的功能角度看，蚯蚓的行为促进了____ 

（3）依据上述实验分析，若在红松林和蒙古栎林中种植一些杨树，有利于增加____ 的数量，从而提高整个生态系统的____

已知向量$\overrightarrow{p}=\left(a_n,n\right),\overrightarrow{q}=\left(a_{n+1},n+1\right)$，（n∈N^*），若a₁=2，且$\overrightarrow{p}\parallel \overrightarrow{q}$，则数列{a_n}的前n项和S_n=（　　）