The correct answer is option 'B' - the back of the tongue tastes bitter.

Explanation:
The tongue is an organ responsible for the sense of taste. It is covered in tiny bumps called papillae, which contain taste buds. Taste buds are specialized cells that allow us to perceive different tastes, such as sweet, sour, salty, and bitter.

There are different types of taste buds located in different areas of the tongue, each sensitive to a specific taste. The taste buds that detect bitter taste are primarily located at the back of the tongue.

The taste buds for bitter taste are concentrated in the circumvallate papillae, which are large, mushroom-shaped papillae found at the back of the tongue. These papillae are arranged in a V-shaped row, forming a border between the back and middle of the tongue.

The bitter taste is often associated with unpleasant substances that may be toxic or harmful, such as spoiled food or certain chemicals. The ability to taste bitterness is thought to have evolved as a protective mechanism to help us avoid potentially harmful substances.

It is important to note that while the back of the tongue is primarily responsible for detecting bitter taste, taste buds for other tastes are distributed across the entire tongue. The front of the tongue is more sensitive to sweet and salty tastes, while the sides of the tongue are more sensitive to sour tastes.

In conclusion, the back of the tongue is where the taste buds for bitter taste are primarily located.