请教rate 和 rates的搭配

twobirds

在OG和GWD中，有几道涉及rate的题，rate做单数是不是就是指“比率”，而作复数rates时，是“fee”的意思，而rates of 和rates for 的意思也不相同。想请教下1）何时用单数还是复数（如果没有谓语动词单复数提示的情况下）；2）何时用rates of 或者rates for?
GWD1-Q34:

Although people in France consume fatty foods at a rate comparable to the United States, their
death rates from heart disease are far lower in France.


A.people in France consume fatty foods at a rate comparable to the United States
, their
B.people in France and the United States consume fatty foods at about the same rate, the

C.fatty foods are consumed by people in France at a comparable rate to the United States
’s, their
D.the rate of fatty foods consumed in France and the United States
is about the same, the
E.the rate of people consuming fatty foods is about the same in France and the United States
, the

OG13的原题：
13. State officials report that soaring rates of liability insurance have risen to force cutbacks in the operations of everything from local governments and school districts to day-care centers and recreational facilities.
(A) rates of liability insurance have risen to force
(B) rates of liability insurance are a force for
(C) rates for liability insurance are forcing
(D) rises in liability insurance rates are forcing
(E) liability insurance rates have risen to force

落薇裳

应该不是这样的吧，虽然我也不太清楚到底怎么判断。
但楼主的第一个例子：
prep笔记上说选项D错误的原因就是单复数，如改为：
the rates of fatty foods consumed in France and the United States are about the same, the
就是正确的，所以rate和rates 的意思应该没有发生太大变化
open to discuss