The statement is true. Dead zones are the zones of oxygen depletion, which is caused by excessive running off of the fertilizers into the water body. These chemicals, particularly the nitrates, which are used by algae etc. which bloom by using the nitrates and use the oxygen present in the water. When they die, oxygen levels become critically low till then, for other aquatic animals like fishes etc., to survive.
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.
It is true that dead zones in waterways can occur as the result of fertilizer runoff.
Stockmanship is a term more common in the beef cattle industry and can be defined as the art and science of handling cattle, or any other farm animal, properly.
