One factor is resting and exercising
stress and peace
It is called a semi-permeable membrane. Most eukaroytic cells have this.
Answer: Four pulmonary veins.
Explanation: Oxygen and nutrient rich blood will flow from the lungs back into this part called the left atrium (Or as some will call it, the left upper chamber in the heart). From there, it goes through four pulmonary veins.
Hope I could help! :)
Well, i took the test and i put artificial selection and got it right. The definition of artificial selection is "The breeding of plants and animals to produce desirable traits" So the answer is A