It is imperative that the students ______ writing their papers by the end of the month.

A．The classical Greeks did not know the existence of suicide.
B．Suicide has always been prevalent in all parts of the world.
C．In today’s society, there are quite a number of people who commit suicide.
D．Nowadays suicide is not as common as it was in the past.

A．For the selection of the responsible persons.
B．For the condition of different group of the women.
C．To see if they were suitable for the space work.
D．To see how they would react to conditions like those aboard the space shuttle.