Final answer:
Without specific context, the instrument played at the festival in the book cannot be determined. However, instruments like flutes and oboes, which use air columns to resonate, or string instruments with resonating sounding boxes such as violins and guitars, fit the description of amplifying sound through resonance.
Step-by-step explanation:
The kind of instrument that is played at the festival, echoing other instances of that instrument elsewhere in the book, cannot be confidently identified without additional context or information about the specific book in question. However, based on the references provided about musical instruments that resonate and amplify sound, it seems that the question is about instruments that use air columns to resonate.
Examples of such instruments include the flute and the oboe, which are wind instruments that amplify tones using resonance in their air columns. Additionally, string instruments like violins and guitars also use air resonance within their sounding boxes to amplify sound, contributing to their overtone structures and characteristic flavors.
The instrument that is played at the festival and echoes other instances of that instrument elsewhere in the book is d) Harmonium. The harmonium is a keyboard instrument that is commonly used in Indian classical music and is also played at festivals. It produces sound by blowing air through reeds when the keys are pressed, creating a harmonious and resonant sound.