Hello Gmat_mission.

Let's take a look at your question.

First, let's rewrite the number 248 as follows $$248=2\cdot124=2\cdot2\cdot62=2\cdot2\cdot2\cdot31=2^3\cdot31.$$ Now, replacing this into the given expression we get $$\left(2^3\cdot31.\right)^{20}=2^{60}\cdot31^{20}.$$ Now, we can see that the units digit of the powers of 2 are:

2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 6
2^5 = 2
2^6 = 4
2^7 = 8
2^8 = 6
.
.
.

Hence, when the power is a multiple of 4 the units digit is 6. Since 60 is a multiple of 4, then the units digit of 2^60 is 6.

On the other hand, the units digit of the powers of 31 are:

31^1 = 1
31^2 = 1
31^3 = 1
.
.
.

It is always equal to 1.

Therefore, the units digit of (2^60)*(31^20) is equal to 6*1=6.

Hence, the correct answer is the option [spoiler]D=6[/spoiler].

I hope it can help you.