Final answer:
Pi (π) is the ratio of a circle's circumference to its diameter, so the correct answer to the student's question is b) Circumference and diameter.
Step-by-step explanation:
The Greek letter π (pi) is used to represent the mathematical constant, which is the ratio of a circle’s circumference to its diameter. Therefore, the correct answer to the question “The definition of Pi (3.14) is the ratio and the relationship of what two measures of a circle?” is b) Circumference and diameter. When using π to calculate the circumference of a circle with radius r, the formula is 2πr. To find the area of a circle, you would use the formula πr². It's important to note that while 3.14 is commonly used to represent π, the actual number extends to an infinite number of decimal places.