Assume that A is a unital separable simple C*-algebra with real rank zero, stable rank one, strict comparison of projections, and that its tracial simplex T(A) has a finite number of extremal points. We prove that every self-adjoint element a in A with τ (a) = 0 for all τ ∈ T(A) is the sum of two commutators in A and that that every positive element of A is a linear combination of projections with positive coefficients. Assume that A is as above but σ−unital. Then an element (resp. a positive element) a of A is a linear combination (resp. a linear combination with positive coefficients) of projections if and only ifτ (Ra) < ∞ for every τ ∈ T(A), and if and only if , whereτ denotes the extension of τ to a tracial weight on A * * and Ra ∈ A * * denotes the range projection of a. Assume that A is unital and as above but T(A) has infinitely many extremal points. Then A is not the linear span of its projections. This result settles two open problems of Marcoux in [30].