农民为农作物施肥的主要目的是为植物的生长提供（　　）

已知等差数列$\left\{a_n\right\}$的前n项和为$s_n$，若$a_1+a_2=5$，$a_3+a_4=9$，则$s_{10}$为（     ）

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。

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。

Dear Mary,

    I receive your E-mail just now. Don't worry about me. I'm getting on well with my research work in the lab. But to my greatly surprise you say you will give up learn English. The reason is because you have not done well in it recently and you have lost interests. I'm afraid I couldn't agree with you . I know it is difficulty to learn English, and English is widely used in the world today. It will be important tool in our future work. Beside, it is becoming more and more important in our daily life. If you study hard, you will be succeed. Do remember that where there is a will, there is a way. I' m looking forward to hearing good news from you.

Yours,

Li Hua

来宾市象州县大力发展养蚕业，“桑基鱼塘”模式在建设新农村中发挥重大作用，该模式获得了鱼、蚕、桑、气的全面丰收．请根据图回答问题．