When source of sound and observer both are moving towards each other, the observer will hear

When a source and observer move toward each other, the relative velocity increases, altering both frequency and wavelength through the Doppler effect.

The apparent frequency is given by $f' = f_0 \left( \frac{v + v_o}{v - v_s} \right)$, where $v$ is the speed of sound, $v_o$ is the observer's speed, and $v_s$ is the source's speed. The positive terms $v_o$ and $v_s$ ensure $\frac{v + v_o}{v - v_s} > 1$, so $f' > f_0$.

Since $v = f\lambda$ remains constant, the wavelength must decrease as frequency increases: $\lambda' = \frac{v}{f'} < \lambda$.

The observer thus hears a high frequency and low wavelength, corresponding to option C.