What might have been discussed before this passage

A．the atmosphere has a lot of water in it when it circulates
B．the water in the atmosphere is purer than that in the world's oceans
C．the amount of water in the atmosphere is greater than that in the oceans in the world
D．the small amount of water in the atmosphere plays an important role in the yearly rainfall

A．To make people believe his description of the beehive.
B．To introduce Karl's observation on bee behavior.
C．To contrast his theories with those of Karl Von Frisch.
D．To support the argument that bees use sunlight to navigate.