The answer is B.
A linear function is a first-order polynomial, which is of the form y = ax + b. It is called first-order because the power of x is 1.
A second-order polynomial is of the form y = ax^2 + b; which eliminates A. This is also known as a quadratic function.
C. can be simplified to y = 2/3 - 7/x, which probably has a name as well.
D. can be simplified to y - y = 3x/8 + 1/8, which is 0 = 3x + 1 or x = -1/3. Not a linear function