MathNet 1999 — Part 01 Question 73

What is the units digit of the number $2^{(2^{1})} + 2^{(2^{2})} + 2^{(2^{3})} + 2^{(2^{4})} + \ldots + 2^{(2^{1999})}$?

(A) 0

(B) 2

(C) 4

(D) 6

(E) 8.