Which is produced by shaking the crumbs off a picnic blanket?
a. a transverse wave
b. a surface wave
c. a longitudinal wave

A. Transverse wave.                          This is because it’s not either of the other two

A a Transverse wave.

Explanation:

A transverse wave is said to be generated whenever the particles of a medium vibrate in a direction perpendicular to the direction of motion of the wave.

When the picnic blanket is shaken the particles of air (the medium  in this case) will move up and down and the transverse wave travels along the blanket , at right angles to the up and down motion of the particles.