Final answer:
The feature in Baroque music that provided harmonic support to the main melody was called b. Basso Continuo, a continuous bass line played by certain instruments along with improvised chords.
Step-by-step explanation:
During the Baroque period, the musical feature that lent harmonic support to the main melodic line of a composition was called Basso Continuo. This was a practice where a bass line was played by instruments such as the cello, bassoon, or keyboard instruments like the organ, harpsichord, or lute, while chords or simple harmonies were played to support the melody, typically improvised according to the figured bass notation. The Basso Continuo is fundamental to the harmonic structure of Baroque music, providing a continuous bass line that underpins the harmony and allows for greater expressivity and complexity in the melodic line.