During contraction of heart muscle cells . A) all of the calcium required for contraction comes from storage in the sarcoplasmic reticulum B) some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores C) the action potential is prevented from spreading from cell to cell by gap junctions D) calcium is prevented from entering cardiac fibers that have been stimulated

C) Some calcium enters the cell from extracellular space and triggers the release of larger amounts of calcium from intracellular stores

Explanation:

The contraction of the heart shows that calcium ions are involved in the contraction of the heart.

When the action potential is generated in the Sinoatrial node, the potential travels down through the cells via the gap junctions. As the potential travels, the calcium stored in the sarcomere is released. These calcium ions along with action potential also move across the cells. So the calcium enters from the space and the some is released from the sarcomere.

Thus, the selected option is correct.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.