Final answer:
Lana is most likely hearing a Gregorian chant in the cathedral, which is a form of monophonic music commonly heard in churches during the medieval period.
Step-by-step explanation:
Lana is most likely hearing a Gregorian chant in the cathedral. Gregorian chant is a form of monophonic music that was commonly heard in churches during the medieval period. It is a sacred genre of music that consists of single melodic lines without any harmonies or accompaniment. The use of Gregorian chant in churches created a solemn and reverent atmosphere and was an integral part of religious ceremonies.