4. Which of the following would be a good reference point to describe the motion of a dog?
a. the ground
b. another dog running
C. a tree
d. All of the above

The correct option is b. another dog running.

The following information should be considered:

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ANOTHER RUNNING DOG

Explanation:

In the given question it is to find a suitable reference point to describe  the motion of dog. Here I could suggest that it is better to compare the dog with  another running dog to create the relative speed difference to get a reliable motion variation.

Because the motion of dog is in the linear with respect to the another dog and to the acceleration produced by the dog in the required interval is easy to calculate with respect to  another dog which is already in motion.

Hence, I suggest that Motion of dog can be analysed better by analyse the motion variation of dog with  another dog running.