If a is an integer, which of the
following could be a4 ?
a. 1.6 x 10^11
b. 1.6 x 10^12
c. 1.6 x 10^13
d. 1.6 x 10^14
e. 1.6 x 10^15

So to work this out we need to find the 4th root of each of those and pick the one that gives an integer.

A:  This is a decimal therefore not an integer.

B:  Again a decimal, therefore not an integer.

C:  This is a whole number, so it is an integer.

D:  Decimal, therefore not an integer

E:  Again a decimal, not an integer.

The only one that gives an integer when put to the 4th root is C, therefore:

could be A^4, as the 4th root of it is an integer.