Question

There are advantage for students to work while 1. _______

There are advantage for students to work while 1. _______
　　studying at school. One of them was that 2. _______
　　they can earn money. For the most part, 3. _______
　　students working to earn money for their own 4. _______
　　use. Earning their own money allow them 5. _______
　　to spend on anything as if they please. 6. _______
　　They would have to ask their parents for 7. _______
　　money or for permission to do things by 8. _______
　　the money. Some students may also to save 9. _______
　　up for our college or future use. 10. _______
第2行为什么把was改为is不是one of 后加复数么.第五行为什么改成allows

Answer 1

把was改为is是因为整篇文章都是用一般时，所以不能突然冒出来一个过去式。
而one of后面加复数指的是of后的名词加复数，正如them；但是谓语是要用单数的，因为one of做主语，不是them做主语。
第五行改为allows是因为earning their own money动名词做主语，所以用单数

Answer 2

单复数看主语，第一个主语是one,第二个主语是动宾短语，都是单数
用is是因为一般现在时

Answer 3

one of。。。意思是。。中的之一，后面谓语用单数，切前面都用的是一般现在式，所以用is。
动名词作主语是单数形式，所以allow后面要加s。