In an Exchange Economy with Only Two Goods, Walras's Law

In an exchange economy with only two goods, Walras's law implies that:

A) both markets cannot be simultaneously in equilibrium.
B) if one market is in equilibrium then the second one must be in equilibrium too.
C) the two markets can be in equilibrium only when indifference curves are smooth and convex.
D) net supply equals net demand at all times.