Which interrogative pronoun best completes the sentence? how is the pronoun used? shirts are still drying on the clothesline? a. whom; object of a preposition b. whose; possessive c. whom; direct object d. who's; subject (in a contraction with a verb)

The answer is B. Whose.

Because A. and C. don't make sense and D. is a contraction. If you used D. it would be like saying "Who is shirts are still drying?" and that doesn't make sense either.  

Whose is used because it is possessive. Your asking "Whose shirts?" The shirts are owned by someone.

postive, comparative, superlative - good, better, best

recall how we defined nouns as words capable of having plurals and possessive endings. adjectives (and their first cousin, the adverb) also have a feature that distinguishes them. they come in three states. first, the raw adjective—in its positive state—merely describes the noun modified; it doesn’t care about how this particular person or thing stacks up against other members of the same noun class