Animals can be classified into two main groups: vertebrates and invertebrates. The main difference between vertebrates and invertebrates is that invertebrates, like insects and flatworms, do not have a backbone or a spinal column. Examples of vertebrates include humans, birds, and snakes.
The answer is : randomization was not used in sample selection. The major difference between experimental and quasi-experimental designs is lack of randomization in sampling selection.
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sorry. I can't not answer this question now cause i already submitted it. i did not mean to.
Photosynthesis occurs in plant cells, but does not occur in animal cells.
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<h2> I don't know but my Answer is </h2><h3>from different environments ,each structure suits their environment better than the other's</h3>
