Final answer:
The difference of two squares can be expressed in the form a² - b². Among the given options, 8x² - 16y² is the difference of two squares.
Step-by-step explanation:
The difference of two squares can be expressed in the form a² - b².
Among the given options, the expression 8x² - 16y² is the difference of two squares because it can be factored as (2x)² - (4y)².
Therefore, option a is the correct answer.