Which of the following is true? a. around 1500ad, the human population began growing more rapidly. b. around 1500ad, the human population began to decrease. c. around 1500ad, the human population began to level off. d. around 1500ad, the human population began to reach carrying capacity.

The human population has not yet reached its carrying capacity, as the population is still growing, even thought this growth does not seem sustainable (since we're destroying the environment on the way).

The population is also not decreasing, nor has it been decreasing in the last time, instead it's increasing. So the correct answer is A.