标准编写中助动词的使用原则有哪些？

A. 预防为主
B. 定期检测
C. 强制维护
D. 防消结合

A. 正确
B. 错误

A. concealed to prevent mechanical damage
B. concealed so the boat can be maintained more easily
C. protected from the weather
D. in an accessible place behind the ceiling