____

已知等差数列$\left\{a_n\right\}$与等比数列$\left\{b_n\right\}$各项都是正数，且$a_1=b_1,a_{2n+1}=b_{2n+1}$，那么一定有（  ）

增加：把缺词处加个漏字符号（∧），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l1处起）不计分。

    Smart-phone apps certainly make our life easier. And now, it look like they could even do our homework for us. Recent years have seen the release of a variety of study aid apps aimed at student. Most of these apps allow users take a photo of our schoolwork and the correct answers will just appear on their smart-phones. Although they are conveniently, these apps present problems to both parents but teachers. Most students just copy the answers from the app, while only a few use the app to study. Better still, some students even use the study aid apps as social networks. But, this isn't to say that study aid apps should be completely banned. Parents and teachers should give necessary guidance to help students take the advantage of the study aid apps' strengths and avoiding their weaknesses.