The correct option is D {1,2,3,4,6,8,12,24,48}
Given A={k:k is a factor of 48}
In roster form:
A={1,2,3,4,6,8,12,16,24,48}
Any set X is a subset of A, if each and every element of X is also an element of A, or if k∈X⇒k∈A.
Now, looking at the options, we can conclude that each set is a subset to A.