麻烦大家帮我看看这个句子吧

The general sales tax has been a major source of income for state governments, many

of which derive more than half of their budgets from it.

后面得定语从句怎么理解，主要是which得指代

这个句子就等于:

The general sales tax has been a major source of income for state governments, and many

of the state governments derive more than half of their budgets from it.