What is a unit of acceleration?

a. m/s

b. m/s2

c. m2/s

d. kg-m/s2

A). m/s ... meters per second.

That's a speed.

b). m/s² ... (meters per second) per second.

Acceleration.

c). m²/s ... square meters per second.

Rate of change of area.

Meaningless unit, unless you happen to be

a painter of houses or a mower of lawns.

d). kg-m/s² ... (mass) x (an acceleration).

This is a unit of force.

In fact, it's the definition of "newton".