A. Combination
B. Single replacement
C. Decomposition
D. Double replacement
Envelope is not essential part of virus (option B)
A virus is a small, infectious agent that can replicate only inside the cells of living hosts. Viruses are not considered living organisms because they do not have their own metabolism or cell structure.
The essential parts of a virus are:
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C. below average values of age tend to accompany below average values of bone density.
D. older women aren't any more likely than younger women to have below average bone density.
Answer: cell cycle
Explanation: