If column #$1$ is decimal, and column #$2$ is binary, what is column #$3?$

$\backslash$table$[[$Decimal$,$Binary Code,$],[0,0,0],[1,1,1],[2,10,11],[3,11,10],[4,100,110],[5,101,111],[6,110,101],[7,111,100],[8,1000,1100],[9,1001,1101],[10,1010,1111]]$

a$.$ Hexadecimal

b$.$ Gray code

c$.$ Twos compliment

d$.$ Biased