Answer: Jennifer [proper] and Julie [proper], her best friend [common], went to the mall [concrete] and look for towels [concrete]. All [collective] the stores had people [collective] in them, despite the lockdown, so they knew the ball was in their court [abstract]. It was a beautiful day [abstract or concrete].
Explanation: The day was beautiful because it was sunny and warm - concrete, facts. It was also beautiful because they had a good time - abstract, not specific. The ball was in their court - abstract because they could then do what they wanted but were not actually playing ball. All and people are collective nouns, more than one but the words do not end in 's'.