Answer to 15 1. When in doubt, drop the pronoun's partner, and it becomes clear. Less refers to quantity, or a volume. Fewer refers to number. It's the old split infinitive.
Proper prepositions prefer to snuggle next to the verb.
Of the products shown, this is one. Neither, the subject, takes a singular verb. Now I lay me down to sleep. Mary's feeling is a state of being. Mary badly misunderstood what I said.