Consider the following 100 sets of 10 elements each:
\{1,2,3, \cdots, 10\}
\{11,12,13, \cdots, 20\}
\{21,22,23, \cdots, 30\}
\vdots
\{991,992,993, \cdots, 1000\}
How many of these sets contain exactly two multiples of 7 ?
Answer Choices
A. 40
B. 42
C. 42
D. 49
E. 50