Consider the following 100 sets of 10 elements each:
\begin{align*}
&\{1,2,3,\cdots,10\}, \\
&\{11,12,13,\cdots,20\},\\
&\{21,22,23,\cdots,30\},\\
&\vdots\\
&\{991,992,993,\cdots,1000\}.
\end{align*}
How many of these sets contain exactly two multiples of 7?<spanclass=′latex−bold′>(A)</span>40<spanclass=′latex−bold′>(B)</span>42<spanclass=′latex−bold′>(C)</span>43<spanclass=′latex−bold′>(D)</span>49<spanclass=′latex−bold′>(E)</span>50