Ralph is looking at a blood vessel under a microscope as part of his study about the cardiovascular system. he notices that the vessel contains blood and has valves. what is the blood vessel that he is observing?
a. capillary
b. vein
c. lymph
d. artery

The right answer is vein (it contains blood and has valves).

The infra-cardiac veins of small and medium caliber possess this system of fight against gravity. The valves consist of a dense connective tissue, surmounted by endothelial cells, corresponding to a fold of the intima. They allow blood circulation in the sense organ / heart but prevent venous reflux.

b. vein

Vein is a blood vessel that exhibit thin muscular walls and it brings the deoxygenated blood  from all the cells, tissues and organs back to the heart. In the veins the valves are present which prevent the backward flow of blood. Lumen of the vein is wide.

According to the above information vein is the correct option.

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.