The correct answer is: d) Polyphonic textures (multiple melodies simultaneously).
Carnatic music is a classical music tradition of South India. It is a monophonic music tradition, which means that there is only one melody at a time. The melody is based on a raga, which is a melodic framework. The rhythm is based on a tala, which is a rhythmic cycle. The melody and rhythm are combined to create a kriti, which is a composition.
Polyphonic music is music that has multiple melodies at the same time. This is not a key element of Carnatic music.