Online shopping is very popular among college students, it is easy, convenient, and often not very expensive.
【正确答案】：Online shopping is very popular among college students because it is easy, convenient, and often not very expensive.
【题目解析】：原句是两个单句，两个独立的单句不能用逗号连接。因此我们可以用because将其处理为原因状语从句。
