Answer:
A.
a formal and serious tone
Explanation:
easygoing.
idle.
inactive.
inert.
lackadaisical.
languid.
lax.
lazy.
dle, indolent, slothful, work-shy, shiftless, loafing, inactive, inert, sluggish, lethargic, languorous, listless, torpid, enervated, slow-moving, slow, heavy, dull, plodding
remiss, negligent, slack, lax, lackadaisical, impassive, good-for-nothing, do-nothing
leisurely
The mood (or tone) of the prologue is considered as sombre, dark, macabre... since from the start we're being told that this story is going to be a story of love, death and loss.
It might be said that the adjective phrase to complete this sentences is option B (across the street) because it is providing information about the apartment, it is modifying the noun. In other cases, they provide more information, "because" is used to give a reason so it would be considered adverbial as well as, "for five years", it is related to time. Option D could be understood as a complement of the noun but not a modifier.
