Final answer:
When the environment has reached its human carrying capacity, it means that it can no longer support further exponential growth of the human population. Options c and d are valid conclusions that can be drawn in this scenario.
Step-by-step explanation:
The carrying capacity of the environment refers to the maximum number of individuals of a certain species that the environment can sustainably support. When the environment has reached its human carrying capacity, it means that it can no longer provide enough resources, such as food, water, and space, to sustain further exponential growth of the human population.
As the human population increases exponentially, the carrying capacity of the environment for humans will decrease (option c). This is because the resources available become limited and cannot keep up with the growing demands of the population. This can lead to severe environmental problems, such as outbreak of diseases, starvation, and conflicts, as mentioned in the reference.
In order to prevent population collapse (option d), humans can try to increase the carrying capacity of their environment by developing sustainable food production methods, improving shelter quality, and managing resources effectively.