Select the best answer for the question. 6. the adjectives these and those should be used only with
a. concrete nouns.
b. plural nouns.
c. simple subjects.
d. singular subjects.

These and those do not work at all with singular nouns, like "these dog." The adjectives can equally be used with "these things", "those ones" or "these dogs". "these ones here" or "those long-haired young labrador puppies" are ok too, so they're not limited to concrete or simple subjects. The subject is always plural, therefore B is the best answer.