Use the table below to answer the next question. to DPMO 3 2700 4 4 63 5 .57 6 .002 A phone service rated at 2.1 million hours Mean Time Between Failure (MTBF) is operating at: O a. less than 3 sigma. O b. between 3 and 4 sigma. O c. between 4 and 5 sigma. O d. between 5 and 6 sigma. O e. better than or equal to 6 sigma