What is the course in the passage about

A．If clouds are high, there will be bad weather.
B．The color of clouds is a factor to help predict the weather.
C．If the weather is good, the clouds must be very low.
D．To study clouds is the only way to understand the weather.

A．learn about the change of weather
B．group them and give them names
C．tell the differences in clouds
D．find the likeness of clouds