Answer:
b. improvisation
Explanation:
Playing by ear is called also improvisation, it means that performing music without notes will generally occur as a skill learned in advanced stages of music training.
The process involves first being able to listen carefully to music while identifying the root notes of the melody.
Then notes can be written down and figuring out a way to interpret them most quickly.
When studying music training of ear is often balanced with music theory, and thus after mastering the notions needed for understanding music. Improvising will turn easier, but there are exceptional cases when people have a perfect pitch.
They can tell quickly which notes and chords are being listened, so they will be able to play spontaneously by ear with little training.