Blood cells are produced in the bone marrow and the bone marrow is part of the skeletal system. So the answer would be skeletal system<em>. </em>
Frogs have very moist skin, when the come in contact with the salt it burns the frog and quickly dehydrates the frog and can result in death for the frog.
<span>The elements that are found in a high proportion in Earth's crust are oxygen, aluminium, iron, calcium, potassium, sodium, and magnesium. But for your Option, I think it is B) Oxygen and Silicon. This is because Oxygen makes 46.6% while Silicon makes 27.7% of the Earth crust.</span>