Let $(M,g)$ be a Riemannian manifold and assume that for all orthonormal $v,z$ the sectional curvatures is bounded from below i.e. $K(v,z) \geq C$, where $C > 0$. Is it in this case possible for the Ricci curvature to vanish? Or is this condition, on the sectional curvature, very strong? Sorry if the question is too trivial :).
Gunam