-Plant cells are more rigid due to the cell wall.
They are both known to be heavy, hydrogen is one of the two stable isotopes of deuterium
I believe the answer is C. They are a type of jelly fish.
A person can only show a recessive trait if both of their parents carried at least one copy of each of the recessive allele. The parents do not need to show the trait, as one copy is not enough to reveal it, but they must both carry it.
Hope this helped!