There are only three autosomal trisomic conditions (Patau, Edward, and Down Syndrome) where a fetus will survive to birth. Why do you think this is so?

An autosomal trisomic condition is the deviation of the chromosome number where an extra copy of the chromosome present with the chromosome pair. The three trisomic conditions are Patau - extra copy at chromosome 13, Edward - extra copy of chromosome 18, and Down Syndrome - an extra copy of chromosome 21

Children or fetuses affected by these trisomies show the least life expectancy and develop as mentally week, other than these trisomies other trisomic conditions are highly lethal so we do not see the survivors and it is due to dosage sensitivity which means that increasing or decreasing their expression levels will reduce cell viability.

d. organisms have cells with different shapes and functions.

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.