Final answer:
Although we can't hear the actual excerpt, based on descriptions, the flute and harp are most likely to produce a light and airy theme. The flute (a woodwind) can deliver high frequency notes embodying 'lightness' while the soft plucking of a harp (a stringed instrument) renders an 'airy' sound.
Step-by-step explanation:
Without the ability to hear the specific excerpt in question, it's difficult to determine which instruments perform the light and airy theme. However, when describing a light and airy sound, the flute and harp are often associated with such tonality. The flute, being a woodwind instrument, can play high frequency notes that are typically described as light, while the harp, a stringed instrument, can create a soft and airy sound when the strings are lightly plucked. Therefore, possibility (a) would be the most likely choice provided that the types of sound we are looking for are indeed light and airy.
Learn more about Instrument Sounds