答案：B

解析：

Option D is correct. If Nate worked 5 times as many hours on weekdays than on weekends, the first equation in the system is x=5y. If Nate made 20 origami figures per hour during weekdays, and 30 origami figures per hour during the weekend, and 650 origami figures the second equation in the system is 20x+30y=650.

Next, substitute 5y for x in the second equation and solve for y to find that the total number of hours Nate worked on the weekend was 5. Then, substitute 5 for y in the first equation and solve for x to find that the total number of hours Nate worked on weekdays was 25. Lastly, find the total number of hours Nate worked during the week by finding x+y=30; that is, Nate worked 30 hours total.