Types of Terms

From the following terms, choose four that are homogeneous and three that are heterogeneous: $-4a^{3}b^{2}$, $6ab^{3}$, $-x^{5}$, $6x^{4}y$, $-2a^{3}x^{4}$, $-ab^{5}$, $4abcx^{2}$, $-2ac$,