A child is practicing scales on his piano. His mother can't wait until he learns some chords so that she can hear several notes together, rather than one note at a time. In psychological terms, the scales are comparable to processes and the chords are comparable to processes.

serial; parallel

Explanation:

Serial and parallel processing are the two processing mechanisms. In serial processing one, abstract or object is processed at a particular time. In parallel processing, more than one or many objects are processed at one particular time. This process continues simultaneously.

As per the given excerpt. the scales that the child is practicing are comparable to serial processing. At the same time, the chords that the child is learning is comparable to parallel processing.

it would be d). more resources must be obtained to attain that combination of goods and services