How do scientist develop scientific explanations about subjects that are impossible to study through controlled experiments?

Research generally supports the theory that caffeine may enhance performance in long distance endurance events. Which of the following is the LEAST likely hypothesis? (a) It may exert a psychologically stimulating effect.

How is the degree of oxygenation of the blood related to skin color?

Witch statement is one of the three parts of a cell theory? A-all cells come from other cells B-cells come from crystals C-cells assemble themselves from whatever is around D-plant and animal cells are exaclty the same

If the earth's tides increased, what would be the most likely explanation?

Which organelle is labeled I?

Which of these is NOT a reproductive isolating mechanism? geographic temporal behavioral all of these are reproductive isolating mechanisms

What type of intrusive igneous rock texture has the largest crystals

Between x = 2 and x = 3, which function has a larger average rate of change than f (x) = 2x has? A) g (x) = (2/3) - x B) k (x) = 5x-2 C) h (x) = 4x-1 D) j (x) = (1/2) - x+1

How can we unlock the 90% of our brain that we never use

Defining neuron, the structure of neurons, the function, and how neurons communicate with each other and the outside world.