A linear function is one of the most simplest form of functions. As the name "linear" indicates, a linear function is simply a line, more precisely a straight line.
So it is in the form of f(x) = ax + b.
Lets now check the possible answers : (second answer :) "a curved line", not correct.
(third answer:) "a parabola", this is not a straight line, so not correct.
(fourth answer:) "a wavy line", not a straight line, so not correct.
The only correct answer is the first one : a line passing through the x axis at negative 2 and the y axis at negative 6.