已知：Ⅰ．常见离子沉淀的pH范围

Ⅱ．焙烧过程中主要发生反应：2FeO·Cr₂O₃+4Na₂CO₃+7NaNO₃=4Na₂Cr₂O₄+Fe₂O₃+ 4CO₂ ↑+7NaNO₂。

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.

柏拉图在《会饮篇》中记载这样一个故事：人最初是球形的，是两个人的合体，能瞻前顾后，任意向前或向后奔跑。众神之王宙斯不能容忍，把人用霹雳劈成两半，让人以后只能用两条腿直着走路，这样人就没有原来那么强大，敬奉神的人数也加倍了。这个故事（    ）

——          ? 

——He is tall and of medium build.