The terrestrial biome in which the average temperature remains low throughout the year is:

Explanation

The correct answer is the tundra. The tundra biome is known for its extremely cold climate, with average temperatures remaining low throughout the year. This is due to its location near the poles and its lack of tree cover, which contributes to its cold conditions. In contrast, grasslands, tropical rain forests, and temperate deciduous forests all experience warmer temperatures at least part of the year, making tundra the unique biome with consistently low temperatures.