distance of r and s from center r^2 + s^2
distance of u and v u^2 + v^2
1...not sufficient ..no u and v present
2....squaring both sides
we get u ^2 = 1+r^2 -2r
V^2 = 1 +s^2 -2s

add them up
u^2 + V^2 = 2 + r^2 + s^2 -2r -2s

clearly not sufficient
put r = 1-s from 1
we get r^2 + S^2 = u^2 +v^2
hence C