12. (12 points) February 6, 2014, was a Thursday, and Xiaopang decided to start practicing calculations from this day (including February 6) and continue practicing until February 17 (including February 17) when school starts. However, if he encounters a Saturday or Sunday in between, Xiaopang still decides to take a break and not practice. It is known that he did 1 problem on the first day, 3 problems on the second day, 5 problems on the third day, and so on. How many calculation practice problems did Xiaopang do during this period?
A. 144
B. 100
C. 81
D. 64
【Answer】Solution: According to the problem, we know:
From February 6 to February 17, there are a total of $17-6+1=12$ (days); among which there are 2 Saturdays and Sundays. Worked for $12-4=8$ (days); completed a total of $1+3+5+7+9+11+13+15=64$ (problems); therefore, the answer is: D.