- 搜標(biāo)題
- 搜題干
- 搜選項(xiàng)
單項(xiàng)選擇題
降落傘火箭信號(hào)的燃燒時(shí)間不少于（）。
A.30s
B.40s
C.50s
D.60s
A.30s
B.40s
C.50s
D.60s
