sales of +noun, 谓语用什么?

题目

sales of +noun, 谓语用什么?
有这么两句话：
1.Sales of CDs 【have】 greatly increased since the early 1990s.
2.She has set a new record, the sales of her latest book【has 】reached 50 million.
sales of的谓语单复数，是不是根据其后名词的单复数判断。还是另有其法？

答案

sales (of...) = the number of the items sold,that is,how many (things) sold + (always) pl.v.
1.have
2.have