Determine whether each of these functions from {a, b, c, d} to itself is one-to-one. a. f(a)=b, f(b)=a, f(c)=c, f(d)=d b. f(a)=b, f(b)=b, f(c)=d, f(d)=c c. f(a)=d, f(b)=b, f(c)=c, f(d)=d