which 就近修饰问题咨询

According to a recent study of consumerspending on prescription medications, increases in the sales of the 50 drugsthat were advertised most heavily accounts for almost half of the $20.8billion increase in drug spending last year, the remainder of which came fromsales of the 9,850 prescription medicines that companies did not advertise oradvertised very little.

我想咨询一下which如果是就近修饰的话，是不是修饰 last year？

就是S+V+O+状语如in 1998， which,which修饰的是状语1998还是S？还是O？