Which equilibrium describes a reversible reaction a short time after starting the reaction with reactants only?

A] N2(g) + 3H2(g)  2NH3(g)

B] N2(g) + 3H2(g)  2NH3(g)

C] N2(g) + 3H2(g)  2NH3(g)

D] N2(g) + 3H2(g)  2NH3(g)

E] N2(g) + 3H2(g)  2NH3(g)