Step 1: Use the flip-flop requirement formula.
The minimum number of flip-flops required is
\[
2^n \geq N,
\]
where \(N\) is the modulus.
Here,
\[
N=10.
\]
Step 2: Determine the value of \(n\).
Since
\[
2^3=8<10,
\]
and
\[
2^4=16\ge10,
\]
the required number of flip-flops is
\[
\boxed{4.}
\]
Therefore,
\[
\boxed{(C)}
\]
is the correct answer.