Answer: in order for a scientific investigation to be valid A hypothesis must be tested throughout a Scientific investigation that can gather evidence and support it.
Explanation: in any scientific investigation you have to have a testable hypothesis, without your hypothesis it’s not really a scientific investigation.
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A) a common ancestor
Homologous structures are structures that are similar in related organisms. There is a basic pattern of bones which can be inherited from a common ancestor
I may be wrong but maybe oil
Answer: Well, populations never evolved than one human might have gone extinct due to many different viruses and sicknesses but other animals might not be extinct. If populations never grew more then that would be because we could not overpower dome viruses. If we never. If we never evolved animals like a Carrier pigeon would not be dead or extinct today.