B. The seasons are caused by the tilt of the Earth on its axis.
If this is a multiple choice question could you list the available answers?
Surely it's D) Simile. It is a figure of speech that is used too compare two states or smth else. You can identify it by the words "like" and "as".
The phrase means that there's a lot of dirt around us and it is a common thing to see that.
