<human>: Q: Along with other factors, how long must a target be engaged to have effective ceiling?
 A: By the late 1930s the British definition was "that height at which a directly approaching target at 400 mph (=643.6 km/h) can be engaged for 20 seconds before the gun reaches 70 degrees elevation".
 Does the answer correctly answer the question

OPTIONS:
- yes
- no
<bot>: yes