Topsoil is the A horizon in figure 7-1.The most leaching of minerals occurs from the A horizon into the B horizon. The C horizon shown in figure 7-1 is most like the parent soil, and <span>the A horizon in figure 7-1 contains the most humus.</span>
So all we know is that the student stated something ("<span>if plants are added to an indoor environment the air quality will improve
"). This is only a statement - it's not a test whether this statement is true yet.
So the correct answer is: it is a hypothesis.
</span>
The replicate DNA fast and reproduce fast by binary fission.
Approximately 4.5 billion years ago
