[单项选择]John can mow a field in 6 hours. Bill can mow a field in 5 hours. Henry can mow a field in 4 hours. Joe can mow a field in 3 hours. Tom can mow a field in 2 hours. If they all work together at their respective rates, how long will it take to mow the field A. 41.4 minutes. B. 39.4 minutes. C. 40.4 minutes. D. 38.4 minutes.