When an individual muscle fiber receives a threshold stimulus, it contracts as much as possible. ... a threshold stimulus is the minimum amount of energy needed to make a muscle fiber contract.
I would say D.....................
Answer:
A plant without fertilizers
Explanation:
A control group is a group where no changes are made so that it can be compared to the group that was tested on, or the independent test variables, to see the difference. So, a plant without fertilizers would be the answer.
<em>hope this helps ♥</em>
Wind and Rain are known to (A), wear down mountains because wind and rain are primary causes of weathering of mountains as well as other natural landforms.