It’s almost certain that the lower-right button is D, but as for B and C, that’s something of a guessing game. The orientation of buttons on doorbells can be confusing. For example, often in two-level buildings the lower-number address is on the bottom, so the numbers align with the vertical hierarchy of the living quarters. Sometimes the buttons in a four-spot setup like this one will run top/bottom, sometimes left side/right side. I don’t think I’ve ever seen them run clockwise or counterclockwise, but such a scenario is likely out there, given how haphazard many urban-apartment doorbells are. That is all presuming there are actually B, C, and D apartments in the building anymore. Maybe the whole place was taken over and turned into a mini-mansion: living large while hiding in plain, determinedly indistinct sight.
An ongoing series cross-posted from instagram.com/dsqt.