The correct option is A A small longitudinal wave will form
When block A is pushed towards right, then due to elastic property of springs, block B will also get displaced to right. Similarly, blocks C and D will get displaced to right.
After a while, all blocks will get displaced towards left and disturbance is transferred towards left.
As blocks are in periodic motion about their mean position along the direction of propagation of wave, we can say that the wave formed is a longitudinal wave.
Since the wave travels in a medium (the springs), it can't be non-mechanical. Also, it's not a three dimensional wave since it travels in the plane of the springs and blocks.
Hence, option (a) is correct.