c
The wavelength of the wave is
$\lambda=\frac{v}{\nu}$
$\lambda=\frac{340}{340}=1 m$
Therefore for different resonances, the required lengths of the air column are
$\frac{\lambda}{4}, \frac{3 \lambda}{4}, \frac{5 \lambda}{4}$ i.e. $25 \mathrm{cm}, 75 \mathrm{cm}, 125 \mathrm{cm}$
As the length of pipe is120cm, the resonance corresponding to $125 \mathrm{cm}$ is not possible.
So, when the water is slowly poured, the first resonance will occur at length
$75 \mathrm{cm}$ of air column. Hence, the height of water is
$h=120-75=45 \mathrm{cm}$