A is the correct choice. It's the reason one might write
[tex]x^2+x+1[/tex]
instead of
[tex]1x^2+1x+1[/tex]
They're both correct, but the 1s in the second form are redundant.
Multiplication by 1 is implied when it's left out. Similarly, we omit 0s when adding. We do this because 1 and 0 are multiplicative/additive identity elements, respectively. In other words, for all complex numbers a,
1 × a = a
0 + a = a
