求教副词问题

哎唷不小心

Most of Portugal's 250,000 university students boycotted classes in a one-day strike to protest a law that requires them to contribute $330 a year toward the cost of higher education, previously paying $7 per year.

• Ayear toward the cost of higher education, previously paying $7 per year
• Byear toward the cost of higher education, for which was previously paid $7 per year
• Cyear, compared to the previously $7 per year, toward the cost of higher education
• Dyear toward the cost of higher education, instead of the $7 per year required previously
• Eyear as opposed to the $7 per year required previously for the cost of higher education
  答案是D

C为什么是错的？我看有解释是说previously是副词，所以不能直接修饰$7.但是我不可以理解为compared to the $7 per year previously吗？副词的位置应该是可以随便放的呀？

请教各位NN，这里应该怎么解释？