The demonstrative pronoun would be those and it would be plural.
The participial phrase in this example is D - stored in the damp basement, as it is both a phrase (doesn't have a verb used with a certain person - stored is participle here, used as an adjective, not a verb) and it has this participle. In the previous options, A - we found - this is not a phrase, here verb is used as a verb, and thus it is a sentence, not a phrase. B - many of the old books - this is a noun phrase, it is about books. C - mold and mildew is an adjectival phrase. And thus, the only plausible answer here is D.
That is odd. Are you requesting that she cover one of your shifts for you?
he tries to sleep it off because he thought he would be back to normal after sleeping