A company has 2 officers processing complaints. Suppose that the time between complaints arrivals at each officers' desks is random and follows an exponential distribution. The distribution for complaints arrivals at officer 1 has lamda = u1 while The distribution for complaints arrivals at officer 2 has lamda = u2. Officer 1 has a probability p1 of referring any request he receives to the supervisor, and officer 2 has a probability p2 of doing the same. What is the average time between request referred to the supervisor?

A: p1/u1 + p2/u2

B: (p1+p2)/(u1+u2)

C: 1/(u1p1+u2p2)

D: 1/(u1p1) + 1/(u2p2)

E: None of the above