Search and Rescue Dogs Read the following excerpt:

Step-by-step, focusing on play-based learning, the dog acquires the techniques needed to find victims. Once the dog learns to find the human without the toy, the trainer will continue working with the dog, hiding the "victim" in more challenging spots, making the trail double back on itself, leaving a trail over a wide range of terrains, or adding another person as a distraction. Trainers also work with dogs in a variety of conditions; rain, snow, and high winds all affect the scent trail. Dogs have to learn how to overcome these conditions to find the scent trail and make the rescue. Trainers spend many hours exposing their SAR dogs to a wide range of situations, terrains, and conditions to make them effective regardless of the rescue situation.

Which of the following explains the central idea in the text above?

SAR dogs are selected for their intense focus.
SAR dogs are trained to handle many circumstances.
Trainers must enjoy working in adverse conditions.
Trainers must be in excellent physical condition.