A reasearcher must only measure one variable at atime,and using a scientific control group gives reliable baseline data to compare their results with.
Answer:
Blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs. Blood leaves the heart through the aortic valve, into the aorta and to the body. This pattern is repeated, causing blood to flow continuously to the heart, lungs and body.
Explanation:
Answer:
Evolution.
Explanation:
It might have acquired the ability to cause disease due to evolution. Due to evolution, the harmless bacteria can turn into infectious pathogens that cause diseases. Evolution is the change in the characteristics of a species over several generations due to the process of natural selection. This evolution in the bacteria occurs due to changing of environmental conditions which changes the genetic makeup of that harmless bacteria and turn into infectious pathogen.
A. The sun, because there has been theory’s of the sun being able to heat earth from there being a lot of iron in the middle of earth.
