In sexually reproducing organisms, why are there exactly two chromosomes in each homologous pair?

Ans.

Sexually reproducting organisms include those organisms, in which both male and female gametes or cells take part in reproduction to form zygote. The zygote develops into an organism that has characteristics of both the parents. Cells of these individuals have two sets of chromosome, one from each parent as they receive genetic material from each parent.

Thus, in these organisms, there are two copies of each chromosomes (or two chromosomes in a homologous pair), since one copy of a chromosome derives from male parent and one from female parent.

i believe the correct answer from the choices listed above is the first option. the scientists need to look at the   validity of data, claims, hypotheses, and observations before  developing an argument. they base their arguments on facts that are present and they make sure they have proofs. 

explanation:

what statement best describes the difference between the sympathetic and parasympathetic nervous systems?

the sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.