【单选题】

When the wind speed decreases to less than 30 knots, you can open the cargo door.

A、You need to open the cargo door when the windspeed exceeds 30 knots.
B、Wait for the wind speed to increase to over 30 knots before opening the cargo door.
C、You are allowed to open the cargo door when the wind speed reduces to less than 30 knots.