An average normal range is between 4,500 and 10,000 white blood cells per microliter
Answer:
<em>Option "A" might be the correct answer</em>
<em>Explanation:</em>
<em>there are some of those viruses where it can be quite potent. Some viruses, such as the rhinoviruses, seldom cause serious illness. But others, such as parainfluenza and respiratory syncytial virus, can lead to severe lung infections in young children.</em>
Crossing over happens in Meiosis 1 only. In Prophase 1 a cells chromatin (chromatin = chromosomes that have not condensed yet) condense and pair up forming homologous chromosomes (paired = XX (2 chromosomes together)). When this happens segments/ alleles of the chromosomes pairing up swap over. This creates genetic diversity as each chromosome is different, it has parts from its pair. This leaves every chromosome unique and individual.
I hope this helps, sorry some of the vocab is rather technical. By the way I would suggest watching the
'Crash Course: Meiosis' on YouTube, this really helped me when I was learning this topic. :D