The answer is basso continuo
From the Italian language sometimes abbreviated as b.c is a technique of self-composition and execution and essential from the Baroque period
The basso continuo is played for one or various instruments, typically and harmonic as the keyboard instruments or others as the harp or lute
with the voice of bass simultaneously in charge of an instrument of grave tessitura like the violoncello, bassoon, the viola da gamba, contrabass and sometimes contrabasso.
It also receives the name of simultaneous accompaniment
I am pretty sure the answer is the second one.
A or d. I feel like it leans more toward d, since it's about the architecture of the building.
