c
\(\begin{array}{l}
Speed,\,V = {\rm{constant}}\,\left( {from\,question} \right)\\
Centripetal\,acceleration,\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,a = \frac{{{V^2}}}{r}\\
ra = {\rm{constant}}\\
Hence\,graph\,\left( c \right)\,correctly\,describes\\
relation\,between\,acceleration\,and\,radius
\end{array}\)