①从图中可以看出，氯元素的最高正价是____。

②若某元素既可显正价，又可显负价，则最高正价与最低负价绝对值的代数和为____。

③写出图中元素的化合价随着核电荷数递增的一条变化规律：____。

如图所示，在竖直向上的匀强磁场中，水平放置着一根长直流导线，电流方向指向读者，a、b、c、d是以直导线为圆心的同一圆周上的四点，在这四点中（   ）

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：在错的词下面划一横线，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。

    When we play football on our school's football field, we have got be very careful. That's because of there is an ancient tree growing in a middle of it. Our school is surround by many historical building. When we decided to turn the only available space into a football field, we find the tree had to be removed. We asked for permission to have it removed anywhere else, and it was too risky because the tree is considered as a national treasure. Final, we decided to build the field around it. I consider the tree as a great symbol of our school.

    Nearly 610,000 Chinese students attended schools and colleges overseas in 2017. China remains the world's ____ (large) supplier of international students. A majority____the students went to European and North American countries. Countries____ (include) in the Belt and Road Initiative (B&R) became new destinations, with student numbers ____ (rise) by 15.7 percent in 2017. At the same time, about 480,000 graduates returned to China. Since 1978, about 5.2 million Chinese____ (study) abroad and among those ____ graduated about 83.7 percent returned to China.

    Meanwhile, a total of 490,000____ (foreign) from 204 countries and regions studied in China is 2017. Students from the Republic of Korea, Thailand and Pakistan were the most numerous, while the United States ranked ____ (four). Students from B&R countries accounted for 64.9 percent of____ total. About 59,000 international students in China ____(support) by Chinese government scholarships.