Final answer:
The central idea in the text is that SAR dogs are selected for their intense focus and ability to learn quickly.
Step-by-step explanation:
The central idea in the text above is that SAR dogs are selected for their intense focus.
The passage explains that after three months of training, the dogs were placed into different categories based on their behavior and abilities. The dogs that advanced to the next level were described as obedient and focused, displaying great promise as service dogs.
Therefore, the central idea is that SAR dogs are selected for their intense focus and ability to learn quickly.