A. 6

A Cube has six faces.

ABCD, EFGH, ADHE, BCGF, ABFE and DCGH are the 6 faces

B. 7

A pentagonal prism has seven faces.

ABGF, AEJF, EDIJ, CDIH, BCGH, ABCDE and FGHIJ are the faces.

C. 4

A Tetrahedron has four faces

OAB, OAC, OBC and ABC are the faces.

D. 6

A pentagonal pyramid has six faces.

OAB, OBC, OCD, OAE, ODE and ABCDE are the faces.