Given a scientific question, generate a correct answer to it.

Input: Consider Input: Observations suggest that a force applied to an object is always applied by what?

Output: another object

Input: Consider Input: All animals have specialized types of what basic structures, which can then do different jobs?

Output: cells

Input: Consider Input: Tropical rainforest, temperate grassland, and tundra are examples of what type of biomes?
Output: terrestrial