well the valid argument forms are used on the ... true questions. And the valid argument forms have both existential and ... example look at this valid argumentform:
OP review the Valid ArgumentForm 4 in the "Some and Most Relationships." The inference (B) in this Q is very clear. (D) is reversal of the first sentence.
Right @nye8870, it's especially helpful for tricky parallel flaw questions! It's best to know that A-->B, B most C, therefore A most C is an invalid argumentform rather than thinking "hmm this doesn't match up with my recollection of valid arguments."