In this addition problem, each letter stands for a different digit.
\begin{array}{cccc}
& T & W & O \\
+ & T & W & O \\
\hline
F & O & U & R \\
\end{array}
If T=7 and the letter O represents an even number, what is the only possible value for W ?
Answer Choices
A. 0
B. 1
C. 2
D. 3
E. 4