why not C?

@Dela, Let's look at (B) and (C). (B) says, "Rent control makes it very difficult for landlords to achieve reasonable returns on any investments in maintenance or in new construction." (B) is great. By putting a cap on what landlords can charge, it's difficult for the landlords to receive any sort of added return for upgrading their properties or constructing new ones. Thus, (B) does a great job at explaining why rent-controlled landlords would be hesitant to build or maintain, so it's the correct answer choice. (C) says, "Rent control is a common practice even though it does nothing to alleviate shortages in rental housing." The problem with (C) is that it does not really do much at all to help explain the landlords' reaction to the rent-controlled policies (it doesn't provide an explanation for why rent-controlled landlords would be hesitant to either build or maintain). Thus, we can get rid of (C). Does that make sense? Let us know if you have any other questions!

Thanks!

@Dela, you're welcome! Let us know if you have any other questions!