Classify each of the following algebraic statements and give a brief justification for your choice.
a. (i) 4x−7=0
b. (ii) 2y2+3y=1
c. (iii) 5=5
d. (iv) 3m+n=12
e. (v) 7p−4=9−p
f. (vi) 9q+6=3q2
g. For each statement, state whether it is A: a linear equation in one variable, B: a linear equation in two variables, C: a non-linear equation, or D: not an equation at all. Give one clear reason for your decision in every case.