Determine whether each of the following relations is an equivalence relation, an order relation, or neither. If it is an order, determine whether it is strict and whether it is partial or total. The universe is the set of positive integers.

a. {hx, yi : y is a multiple of x}
b. {hx, yi : the greatest common factor of x and y is 5}
c. {hx, yi : x and y have the same number of prime factors}
d. {hx, yi : when written in base 10, x has at least as many digits than y}