A conical tank has height m and radius m at the base. Water flows at a rate of m/min. How fast is the water level rising when the level is m and m?
a) a = height, b = radius, c = flow rate, d = height and radius at the given level
b) a = m, b = m, c = m/min, d = m and m
c) a = m, b = m, c = m/min, d = m and m
d) a = m, b = m, c = m/min, d = m and m