7. Given that $A, B, C, D, E, F$ are real roots and $D \neq 0$, let

Proposition A: $A=C$ and $B=0$;
Proposition B: $A x^{2}+B x y+C y^{2}+D x+E y+F=0$ is the equation of a circle. Then Proposition A is a ( ) for Proposition B to hold.
A. Sufficient and necessary condition
B. Sufficient but not necessary condition
C. Necessary but not sufficient condition
D. Neither necessary nor sufficient condition
7. C. If $A x^{2}+B x y+C y^{2}+D x+E y+F=0$ represents the equation of a circle, then it must be that $A=C$ and $B=0$, but the converse is not necessarily true, hence the answer is C.