Answer: A. Diseases will increase.
Step-by-step explanation:
The carrying capacity can be define as the maximum number of the population of species that an ecosystem can support in terms of availability of resources. When the population of the species exceeds the carrying capacity, the population of the species starts declining.
When the human population met the carrying capacity, the diseases will increase as the transfer of pathogen will become easy and the resources to cure the population will be limited.