A) atoms at [0.5, 0.5] and [0.5, 0]
B) a1 = 3 A, a2 = 3 A, phi = 60; and atom at [0, 0]
C) a1 = 3 A, a2 = 5.196 A, phi = 90; and atoms at [0, 0] and 0.5, 0.5]
D) No way!