If the arrival rate of units is X and the service rate is u for a waiting line system having 'm' number of service stations, then the probability of services unit being turned out in the time interval, \[(t+\nabla t):\]

• A. Zero
• B. \[\mu .\nabla .t\]
• C. \[m\,\mu .\nabla .t\]
• D. \[n\,\mu .\nabla t\]