**Answer:**

The acceleration of textbook is downward at the slowest rate.

(a) is correct option.

**Explanation:**

**Given that,**

The object is accelerating downward at the slowest rate.

(a). a textbook falling onto the surface of the moon

(b). a flower pot that has been pushed out a window

(c). a pebble falling off a cliff through the air

(d). a baseball thrown from third base to first base

**We know that,**

**Acceleration :**

Acceleration is the product of mass of object and gravity.

**We need to find the accelerating downward at the slowest rate**

**According to given data,**

Acceleration depends upon weight and gravity.

We have some example of free fall.

(b), (c) and (d) are the example of free fall.

In which the gravity is same.

But in option (a) textbook falling onto the surface of the moon

**We know that,**

The gravity on the moon is less than the earth.

**So,** we can say that the acceleration of textbook is downward at the slowest rate.

**Hence, The acceleration of textbook is downward at the slowest rate.**

**(a) is correct option.**