<span>sexual reproduction</span><span>
Sexual reproduction provides genetic variation because the sperm and egg that are produced contain different combinations of genes than the parent organism. Sexual reproduction involves meiosis which is the process of a cell doubling its DNA, shuffling its genes and then dividing the shuffled DNA among four cells.</span>
The correct answer is - D) covered by warm shallow seas.
The fact that the crinoids are have an abundance in the fossil records in Pennsylvania in the Mississippian Period, tells us that this area was covered with shallow and warm seas. The reason why we can get that conclusion is that the crinoids live only in that kind of environment, so it simply a logical conclusion.
The geological data is also confirming this, as it is easily noticeable in the layers that during this period of the geologic past, what is now Pennsylvania, was covered with shallow sea waters. Also, this waters were warm too, as the climate was warm and humid and that period, so it was a perfect environment for the crinoids to flourish.
