If r = 199,999 and s = 991,999, which of the following is the units digit of r^4 + s^4? Choose the correct answer
A) 0	B) 1	C) 2	D) 8	E) 9
The exponents of 9 cycle between 9 (odd exponents) and 1 (even exponents).   Then the sum of r^4+s^4 will have the units digit of 1+1= 
<gadget id="calculator">1+1</gadget>
<output>2</output>
2 as a units digit.   The answer is 2.
<result>C</result>
If r = 199,999 and s = 991,999, which of the following is the units digit of r^4 + s^4?