Final answer:
The guitarra, a type of string instrument, was the plucked instrument used to accompany Renaissance secular songs. Its use of resonance and vibrating strings amplified and enriched the sound, making it popular during this period.
Step-by-step explanation:
The plucked string instrument used to accompany Renaissance secular songs was the guitarra (option c). The guitarra, like other string instruments such as violins and guitars, use resonance in their sounding boxes to amplify and enrich the sound created by their vibrating strings. The bridge and supports couple the string vibrations to the sounding boxes and the air within. This leads to the enchanting sound we associate with these instruments. Notably, the guitarra was notably popular during the Renaissance period.
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