选择题：It() as a shock to realize that I was not alone in the room.

Heart disease is one of the() causes of death.

Great changes are in prospect in this area ()foreign investment.

Her parents died when she was a baby and she was brought() by her aunt.

Human behavior. is mostly a product of learning ()the behavior. of animals mainly depends on instinct.

It is said that() boys in your school like playing football in their spare time, though others prefer basketball.