The correct answer is option 'A' - Nerve cell.

Explanation:
The nerve cell, also known as a neuron, is the largest cell in the human body. Here's why:

1. Structure: Nerve cells have long, branch-like structures called dendrites that receive signals from other cells and transmit them to the cell body. The cell body contains the nucleus and other organelles necessary for the cell's functions. From the cell body, a single long projection called an axon extends to transmit signals to other cells. This axon can be extremely long, reaching several feet in length in some cases.

2. Length: Nerve cells can vary in size, but some can be quite long. For example, the neurons that extend from the spinal cord to the toes can reach lengths of up to three feet. This makes them the longest cells in the human body.

3. Function: Nerve cells are responsible for transmitting electrical signals and coordinating communication throughout the body. They play a crucial role in the nervous system, allowing us to think, move, feel, and perform various bodily functions.

4. Specialization: Nerve cells have specialized structures and processes that enable them to carry out their functions effectively. They have dendrites that receive signals, an axon that transmits signals, and synapses that allow communication between neurons.

5. Complexity: Nerve cells are highly complex and have intricate networks of connections with other cells. They can form complex circuits and pathways in the brain, allowing for sophisticated processing and integration of information.

Overall, nerve cells are the largest cells in the human body due to their long axons and extensive connections. They are essential for the functioning of the nervous system and play a crucial role in coordinating various bodily processes.