A Company Wishes to Monitor the Variation in the Length $\bar{x}$

Multiple Choice

A company wishes to monitor the variation in the length of time it takes to process and send a bill to a customer.Seven bills will be randomly selected each day for a 60-day period and the length of time it takes to process and send the bill to a customer will be recorded for each bill.The appropriate control chart is a(n) :

A) $\bar{x}$ -chart.
B) R-chart.
C) p-chart.
D) u-chart.