Strenuous muscular is just a fancy way to say exercise. As the muscles are used more often the need more oxygen, so that is why your breathing rate increases while doing "exercise".
Answer:
B. Virus
Explanation:
Once attached to a host cell, a virus injects its nucleic acid into the cell. The nucleic acid takes over the normal operation of the host cell and the host cell produces multiple copies of the virus.
Well in the scientific method you have to observe, hypothesis, prediction, experiment and conclude. So will you provide the answers if there is any multiple choice questions please post so I can help more.
Metaphase I: The tetrads of chromosomes are lined up on the equator of the cell with the spindle apparatus having already been completely formed. It is during prophase I and metaphase I where genetic recombination occurs.