**Explanation:**

**Alveoli** are tiny air sacs present in the lungs that play a crucial role in the process of respiration. They have several characteristics that make them suitable for their function. Let's discuss each option and determine which one is not a characteristic of alveoli:

a) **Thin membrane**: Alveoli are lined by a thin membrane called the alveolar epithelium. This thin membrane allows for efficient gas exchange between the air in the alveoli and the surrounding blood capillaries.

b) **Balloon-like structures**: Alveoli have a balloon-like structure that allows them to expand and contract during the process of breathing. This expansion and contraction help in the exchange of oxygen and carbon dioxide between the lungs and the bloodstream.

c) **Small surface area**: This option is the correct answer. Alveoli actually have a large surface area despite their small size. The combined surface area of all the alveoli in the lungs is roughly equivalent to the size of a tennis court. This large surface area maximizes the contact between the air and the blood, facilitating efficient gas exchange.

d) **Surrounded by a rich network of blood capillaries**: Alveoli are indeed surrounded by a rich network of blood capillaries. This arrangement allows for the exchange of gases between the air in the alveoli and the blood in the capillaries. Oxygen from the air diffuses into the bloodstream, while carbon dioxide from the blood diffuses into the alveoli to be expelled during exhalation.

In conclusion, the characteristic of alveoli that is not accurate is option c) "Small surface area". Alveoli have a large surface area that enables efficient gas exchange during respiration.

A typical pair of human lungs contain about 700 million  alveoli, producing 70m2  of  surface area. Each  alveolus  is wrapped in a fine mesh of capillaries covering about 70% of its  area....so "C" is correct..