C. If 'A' is the effect but 'B' is not its immediate and principle cause.
Feedback Events (A) and (B) are related events and chronologically (B) occurs before (A) and because of as they are planning to increase capacity, they have to make a plan to sell their products also so they open new offices for marketing those products. But opening an office in a particular city, requires other events such as market survey etc. It is not the immediate and principle cause.