$3.$ Argument: Some cashmere sweaters are fashionable garments, so some cashmere sweaters are not

suede jackets, for some suede jackets are not fashionable garments.

$3\mathrm{.}1$ The form of this argument is:

a$.$ Some C are F$.$ b$.$ Some S are not F$.$ c$.$ Some S are not F$.$ d$.$ Some F are not S$.$ e$.$ Some C are F$.$

Some C are not S$.$ Some C are F$.$ Some C are not S$.$ Some F are C$.$ Some F are not S$.$

Some S are not F$.$ Some C are not S$.$ Some C are F$.$ Some S are not C$.$ Some C are not S$.$

$3\mathrm{.}2$ Which of the following substitutions proves the argument invalid?

a$.$ C$=$ animal, F$=$cats, S$=$mammals b$.$ C$=$dogs, F$=$animals, S$=$mammals