According to Pi, a zookeeper will know he or she has created a healthy environment for the animals WHEN THE ANIMALS REPRODUCE.
For animals to reproduce and give birth to young ones, many things has to be in place, such as suitable partners, right environment, right food, etc. Animals naturally reproduce when the environment is favorable unto them. Thus, reproduction of animals in the zoo shows that the right environment has been created for the animals.
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I believe the answer is B. They would be led to the promised land if they obeyed God
The action of the speaker that can be considered ironic is that actually the speaker takes initiative of establishing the wall up to himself but then he questions it and has some doubts about that. There is another irony, I would say, the main one, you may find it useful : the wall which was meant to separate neighbours brings them together every year in order to repair it. Is it really the borderline?Hope that helps.