This letter also provides procedures that can be used to help mitigate moisture ingress into the connector cavity until such time that the moisture problem can be resolved and a service bulletin is available to correct the problem.
答案解析
解析：
这封信提供了可以用来帮助减轻连接器腔内湿气进入的程序，直到湿气问题得以解决并且有一个服务公告可用来纠正问题。选项A表明，如果有一个可用的服务公告来纠正连接器腔内湿气进入的问题，那么这封信就会变得无用。因此，选项A是正确的。
举例来说，就好像你的手机出了问题，但是厂家已经发布了一个修复方案，那么你之前收到的关于手机问题的说明书就变得没有用处了。因为你可以直接按照厂家的修复方案来解决问题，不需要再参考之前的说明书。
相关知识点：
信件提供防湿气进入连接器程序
相关题目
Adjust the potentiometer until you do not hear a hum from the loudspeaker.
The title page shall contain the airplane serial number and registration number if appropriate.
If you install the upper drag strut with the head down, it will hit the lower drag strut during retraction.
Make sure that the indication on the gauge agrees with the quantity that is in the tank.
If the scratch does not go through the protective layer, the unit is serviceable.
When a fire starts, the temperature increases and causes the detector to operate.
Make sure that the fluid that goes through the tube has no bubbles.
Apply a corrosion inhibiting compound into the affected area to stop the corrosion process.
Use caution to assure that probe is as close as possible to antenna base of panel without touching antenna.
The installation of a split scraper ring is also a temporary repair and should be replaced when the nose landing gear is disassembled for other maintenance or overhaul.
