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:
![y=\sqrt[]{1-x^2}](https://img.qammunity.org/2023/formulas/mathematics/high-school/8zn8z6512fdr9lczd2tw2jegh9anis7jg0.png)
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