A particle is executing uniform circular motion with velocity $\overrightarrow{\mathrm{v}}$ and acceleration $\overrightarrow{\mathrm{a}}$. Which of the following is true?

In uniform circular motion, velocity magnitude |v| = constant but direction of velocity keep changing. Centripetal acceleration always directed towards centre; hence, its direction keeps on changing.
Hence, both $\overrightarrow{v} \text{and }\overrightarrow{a}$ are not constant.