Some apartments of the early 1900's were known as dumbbell tenements because they had

Its A. Few windows and no ventilation

Explanation:

B, C, and D are all things good houses and homes have, for the wealthy or even middle class. But tenements were for the working poor and people who did not have a lot, these homes were cramped, small, dirty, dangerous, and many had no windows or air flow. Thus it is A.