已知函数f（x）=x﹣alnx（a∈R）

春秋战国时期的土地利用率和农作物产量显著提高,主要是因为（    ）。  

短文改错：假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。
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。
    It was 7:15 in the morning of February 8, 2007. I was walking along Park Road towards the east while an old man came out of the park on the other sides of the street. Then I saw a yellow car drive up Third Street and made a right turn into Park Road. The next moment the car hit the man while she was crossing the road. He fell with a cry. The car didn't stop and drive off at full speed heading west. I noticed the driver was young woman wore a pair of glasses and the plate number was AC864. After two minutes later, I stopped a passed car and took the old man to the nearest hospital.

氯化二硫(S₂Cl₂)是广泛用于橡胶工业的硫化剂，其分子结构如下图所示。常温下S₂Cl₂是一种橙黄色的液体，遇水易水解，并产生能使品红褪色的气体。

下列说法错误的是(      )

小明在探究“物体的重力势能与哪些因素有关”的活动时，用长铁钉子做成的四脚小方凳、不同质量的砂袋和一盆细砂，做了以下实验，如图所示，比较分析后回答问题。