D. <span>controlled
is the right answer because a</span><span>n </span>experiment<span> in which an observer tests a hypothesis by looking for changes carried by alterations to a variable.</span>
Mitochondria is described as the power house of the cell, because it is the cell organelle that process the production of ATP, which is the energy source of the cell. Kreb's cycle occurs in the mitochondria, it is the process by which energy is generated inside the cell, leading to the production of ATP and carbon dioxide and water are given up as waste products.
Geothermal energy comes from the heat within the earth. The word "geothermal" comes from the Greek words geo, meaning earth," and therme, meaning "heat."
