Answer:
hydroshpere and biosphere
Explanation:
it contains
hydrosphere: cleaning of water
biosphere: helps plants and animals
The answer is <span>Time is the independent variable, and the number of birds is the dependent variable. </span>
<span>An independent variable is variable that is not affected in the experiment. It is what experimenter controls. On the other side, a dependent variable is called dependent because it depends on the independent variables. It is what is affected during the experiment.
In Sam investigation, he controls time - he counts birds at 6 a.m. and 6 p.m. So, time is the independent variable. The number of birds is affected during the experiment, so it must be the dependent variable.
</span>
<span>The answer is valves. One </span><span>feature that the entrances and exits to the heart need in order to maintain this flow pattern is the valves. E</span><span>ntrances and exits to the heart may need valves in order to maintain this flow pattern. There are valves that control blood flow to the ventricles, and valves that control blood flow out of the ventricles.</span>
