6. Teacher Zhang runs for 20 minutes every Monday, Saturday, and Sunday, and jumps rope for 20 minutes every other day. In a certain month, he ran for a total of 5 hours. So, the 10th day of this month is ( ).
(A) Sunday
(B) Saturday
(C) Tuesday
(D) Monday
【Answer】D
【Analysis】This month, a total of $5 \times 60=300$ (minutes) were spent running, and each week, $20 \times 3=60$ (minutes) were spent running. Since $300 \div 60=5$, there are 5 Mondays, Saturdays, and Sundays in this month. A regular month has at most 4 weeks and 3 extra days, so it can be concluded that this month has 31 days, and the first day of the month is a Saturday. According to the periodicity, it can be determined that the 10th day of the month is a Monday.
【Difficulty】
【Knowledge Point】Cycle Problems