It means , one , only , single .. hopes this helps
The
Thymocyte progenitors enter the subcapsular region of the thymus as
double-negative cd3- t cells where the double negative refers to lack of
cluster determinants CD4 and CD8. Double-negative cd3- t cells exist as small population
that is 1%-5% of lymphocytes in the lymphoid organs and peripheral blood of
humans and normal rodents.
It is a controlled experiment as everything is the same apart from one variable
The theory of evolution will be best supported by the evidence showing a species changes over time. Thus, option A.
Basic evidences for proving the theory of evolution are anatomy, Biological morphology, Fossils and direct observations. There have been various theories for the proof of evolution like structural similarities in an embryo formation pointed towards common ancestors. Theory of Natural selection embarked by Charles Darwin to show genetic variations picked by organisms in whole population.
The most authentic theory over evidence for evolution is Paleontological theory which includes study, observation and acquired prove of fossils of various organisms in the forms of Petrified, mold and cast, trace fossils, compression fossils, impression fossils, etc.
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hope that helped you on your journeys