If in Python we define

$a=[1,2]$

and

$b=[3,4],$

what will be the result if we enter

$a+b?$

Note: This is not a math question. It is supposed to highlight the crucial distinction between common sense and python'syntax.

$[3,4,1,2]$

$6,4$

$1,2,3,4$

$4,6$