Passage Summary: Acting 'flexibly' instead of just by instinct requires a huge amount of brain cells—more than any insect actually has in its tiny brain.

Reasoning: Flexible behavior requires a high number of neurons, but no insect brain is large enough to contain that many neurons.

Analysis: This is a formal logic problem involving a necessary condition. The stimulus establishes that a large number of neurons is a requirement for flexible behavior. It then provides the fact that insects lack this large number of neurons. Therefore, we can deductively conclude that insects are incapable of flexible behavior. When looking for the 'Must be True' answer, avoid any choices that go beyond this simple synthesis, such as those discussing the evolution of insects or the benefits of instinct.