二人做功之比 W甲 W乙 = G甲h G乙h = G甲 G乙 = 5 6 ；所用时间之比为 t甲 t乙 = 9s 10s = 9 10 ；所以甲、乙二人爬杆的功率之比是 P甲 P乙 = W甲 t甲 W乙 t乙 = W甲 W乙 × t乙 t甲 = 5 6 × 10 9 = 25 27 ．故选C．
