The underlined word "blurred" in the 3rd paragraph most probably means ______.

A．Mate selection is exclusively based on love.
B．Mate never refers to the person whom one intends to marry.
C．Economic factors are rarely taken into consideration in mate selection.
D．To nontraditional people mate is more than a person’s intended spouse.

A．theories of its origin and history are varied
B．our knowledge of it is highly insecure
C．only a very small sample of it has been observed
D．few scientists are involved in the study of astronomy