Could be false. The stimulus never has “pet stores in West Calverton that are not independently owned” as a sufficient condition, so we can’t make any valid inferences about the percentage of those stores that do or don’t sell exotic birds.

Could be false. As shown below, answer choice (B) is a conditional statement that uses “tropical fish and exotic birds” as its sufficient condition. But the stimulus doesn’t say anything about pet stores that sell tropical fish and exotic birds!

Could be false. All we know about pet stores in West Calverton that sell gerbils is that they’re not independently owned. We have no information about whether or not some might also sell exotic birds!

Must be true. As shown below, by chaining the conditional claims, we see that “not selling tropical fish or selling exotic birds” is a necessary condition of being an independently owned pet store in West Calverton.

Could be false. Any independently owned pet store in West Calverton must either not sell tropical fish or sell exotic birds, but that means these stores could do any of the following: not sell tropical fish, sell exotic birds, or both sell exotic birds AND not sell tropical fish.