The correct options are
A x, y, z, u are in H.P. for infinite possibilities of a, b, c and d.
B x, y, z, u may be in A.P. for some value of a, b, c and d.
C x, y, z, u may be in A.G.P. for some value of a, b, c and d.
⇒ax=ay.ry=az.r2z=au.r3z=K⇒x=logaKy=logaK1+logarz=logaK1+2logaru=logaK1+3logar
⇒ x, y, z, u are in H.P.
⇒ x, y, z, u may be in AP./A.G.P.
for a = b = c = d = 1.