Let L(k) denote the arc length of the graph of y=kx2 for 0≤x≤1, where k>0. Which of the following statements about L(k) is true?
a) L(k) is the same for all positive k.
b) L(k) is directly proportional to k.
c) L(k) increases as k increases.
d) L(k) increases for 0<k<1 and decreases for k>1.