In Rt△ABC, AB= 15 step, BC=8 step, and the radius of inscribed circle is R. AC = ab 2+BC 2 =152+82 =17 (pythagorean theorem), and s △ ABC =/kloc-. BC，S△ABC = S△AOB+S△BOC+S△AOC = 1 2 AB？ R+ 1 2 BC? r+ 1 2 AC？ r = 1 ^ 2(a b+ BC+AC)r，∴ 1 ^ 2 ab？ BC = 1 ^ 2(a b+ BC+AC)r，∴r= AB？ BC AB+BC+AC = 15？ 8 15+8+ 17 = 3.∴ The diameter is 6. So I chose D.