A linear function has this form:
Notice that option A cannot be written in this form, because x and y have a square power. If you clear y you'll get:
Option B you can write it in the form of a linear equation:
For this option, a = -1 and b = 14
Option C cannot be written in this form:
And option D can be written like that:
Here, a=6 and b=3.
So, options B and D are linear equations