d
In three seconds, the distance travelled by wave=1 $c m / s \times 3 s=3 c m$
Hence the center of the wave, the crest, reaches the point $O '$ in the time.
The amplitude of the wave becomes $1 \mathrm{cm}+1 \mathrm{cm}=2 \mathrm{cm}$
Hence correct answer is option $D.$