【单选题】

Due to frequent changes in, or varying combinations of, some types of equipment such as avionics and instrumentation, one or more separate documents for these products may be requireD.

A、One or more separate documents for some types of equipment such as avionics and instrumentation may be required because they change frequently or they have various combinations.
B、Some types of equipment such as avionics and instrumentation are changed regularly or combined in different forms, requiring to have one or more separate documents.
C、Some types of equipment such as avionics and instrumentation are often revised or combined differently to require one or more separate documents.