Answer:
A. 5 is the base
D. 12 is the exponent and tells us how many times we should multiply 5 by itself
Explanation:
The given expression is

This is a number written in an index notation.
The base is 5.
The exponent is 12.
The exponent tells us how many times the base multiplies itself.
Therefore
means, 5 multiplies itself 12 times.
Options A and D are correct.