Car A is going straight, Car B going in the opposite direction make a left turn. They
Crash. Who's fault?

We need more details.

Are there any street signs? Are there any traffic lights? If yes; what color(s) are they in which direction? Are there any green arrows? Are there any Police directing traffic? Please, for the love of Pete, provide a little more information.

Seriously... how many sides does a circle have?

Generally a car making a turn has to yield to traffic going straight. But as noted, there is not enough info here to make a judgment.

Agreed. Are they at intersection? On road?

But in general, a car turning has to yield to on coming traffic.