D:
a,b,c are inherently bad or simply not helpful
Answer: (A) The conclusion is valid because the independent and dependent variables in experiment were controlled.
Explanation: There are some basics requirements in order for an experiment to be valid: hypothesis, monitoring, independent and dependent variables and constants.
Answer: Valves in the veins
Explanation: The flow of the blood inside the body takes place through the veins and arteries. The oxygenated blood from the heart is supplied to the different parts of the body.
The blood flows from the capillaries to the venules and from there to the veins. The blood moves in the veins by the rhythmic movement of the smooth muscles in the body.
Most of the blood moves against the gravity so there is a chance that it can backflow so to prevent this there are valves in the veins known as one way valves.
No, producers produce their own food like plants that use photosynthesis to produce sugar whilst aphids cannot produce their own food and have to feed of other plants.
Squamous cells area one single layer and flattened, this allows for diffusion of oxygen and carbon dioxide to happen easily in the lungs.
