On this monthly calendar, the date behind one of the letters is added to the date behind C. If this sum equals the sum of the dates behind A and B, then the letter is:
\begin{array}{|c|c|c|c|c|}
\hline
\text{Tues.} & \text{Wed.} & \text{Thurs.} & \text{Fri.} & \text{Sat.} \\
\hline
& & C & A & \\
\hline
& & Q & & \\
\hline
S & B & P & T & R \\
\hline
\end{array}
Answer Choices
A. \mathrm{P}
B. \mathrm{Q}
C. R
D. \mathrm{S}
E. \mathrm{T}