The correct answer is option 1: Nerve cell.

Nerve cells, also known as neurons, are the largest cells in the human body. They have long extensions called axons and dendrites that allow them to transmit electrical signals over long distances. The axons can be several feet long, making nerve cells larger than any other cell in the body.

Option 2: Muscle cells are not the largest cells in the human body. While they can be quite long, especially in skeletal muscle, they are generally not larger than nerve cells.

Option 3: Liver cells, also called hepatocytes, are of average size compared to other cells in the body and are not the largest.

Option 4: Kidney cells, specifically the cells of the renal tubules, are also not the largest cells in the human body. They play a role in filtering waste products and maintaining electrolyte balance in the kidneys.

Therefore, the largest cell in the human body is the nerve cell or neuron.