The ones digit of the product is the same as the ones digit of $$0^{4}$$, $$1^{4}$$, $$2^{4}$$, $$3^{4}$$, $$4^{4}$$,  $$5^{4}$$, $$6^{4}$$, $$7^{4}$$, $$8^{4}$$, or $$9^{4}$$. The ones digit can be $$0$$, $$1$$, $$5$$, or $$6$$. 
I multiply a whole number by itself, then multiply that product by itself. The ones digit of my final product cannot be． 

a. $$1$$ 
b. $$4$$ 
c. $$5$$ 
d. $$6$$ 