Where does my trash go after it leaves my house?
After you answer this question, look at the picture and talk about this idea. (The picture may be confusing: the idea is trash in a volcano.)
We must postulate/posit ideas before we can test them and then make use of them! Making use of them is the goal.
FYI:
postulate-
v. suggest or assume the existence, fact, or truth of (something) as a basis for reasoning, discussion, or belief.
posit-
v. assume as a fact; put forward as a basis for argument
The Daegou landfill is in 광천동.
Also sewage tree ment plant is in 광역시.