Question

what is the characteristic feature of the tundra biome?permafrostheavy precipitationwarm temperaturesdense vegetation

Explanation:

The Tundra biome is known for its cold climate. Permafrost (permanently frozen ground) is a key feature. Heavy precipitation is not typical (it's usually dry). Warm temperatures are incorrect (it's cold). Dense vegetation is also wrong (vegetation is sparse due to harsh conditions).

Answer:

permafrost