Consider a correctly-specified demand-supply system: q = a-,p + l + L" and p = a-uq + 21Z1 + -az-z + 112, where (q, p) are respectively the logarithms of traded quantity and price of a commodity, (Zl, z2) are observed variables that are uncorrelated with the unobserved error terms (L.'l, 1/2), (a-I, ll, CQ, 1321, are constant parameters, and 1 a-laz 0. The second equation is identified when 0 0 C) b. d. or-Oand r-Oand