单选题

$a={a,b,c} $b={a,b} $c=$a+$b...

Question

	$a=['a','b','c']



	$b=['a','b']



	$c=$a+$b

则$c等于：

A. {a,a,b,b,c}

B. {a,b,c}

C. {a,b,c,a,b}

D. {a,c,a,b}