The lin-of-sight communication requires the transmit and receive antennas to face each other. if the transmit antenna is vertically polarized, for best reception the receiver antenna should be

a) horizontally polarized

b) vertically polarized

c) at 45^o with respect to horizontal polarization

d) at 45^o with respect to vertical polarization

Both the antennas should have the same polarization in order to  have best reception

So answer is

b) vertically polarized