Step 1: Apply the Mean Value Theorem.
For the function \( f(x) = \log x \), the Mean Value Theorem applies when the derivative of the function equals the difference in function values divided by the interval length.
Step 2: Conclusion.
Thus, the correct value of \( c \) is \( \log 2 \).
Final Answer:
\[
\boxed{\log 2}
\]