A. 5% B. 10% C. 30% D. 50%
A. 鸣30s、停、鸣30s、停、鸣30s B. 鸣20s、鸣10s、停、鸣20s、鸣10s、停、鸣20s、鸣10s C. 鸣10s、停、鸣10s、停、鸣10s D. 鸣20s、停、鸣20s、停、鸣20s