Final answer:
A typical acoustic guitar has six strings, and when plucked, standing waves occur in the guitar string and the air inside the guitar.
Step-by-step explanation:
A typical acoustic guitar has six strings. The question asks for the number of strings on such a guitar, with options being 7, 6, 8, and 9. The correct answer is (b) 6 strings. These six strings are typically tuned to the standard notes of high E, B, G, D, A, and low E and are designed to create standing waves when plucked.
When a musician stands outside in a field and plucks an acoustic guitar string, standing waves will most likely occur in the guitar string itself (a) and the air inside the guitar (b). These standing waves are the heart of the sound production in string instruments.