Final answer:
Psychoactive drugs are the correct answer as they can significantly alter states of consciousness by changing the function of the brain, affecting mood, thinking, perception, and behavior. Thus, the correct answer is option d.
Step-by-step explanation:
The question asks about which of the following properties can alter one's state of consciousness. Among the options, psychoactive drugs are the agents that can significantly alter states of consciousness. These substances change the function of the brain, leading to modifications in mood, thinking, perception, and behavior. For example, psychoactive drugs can be found in prescription medications like opioid painkillers, legal substances such as alcohol and nicotine, and illegal drugs like LSD and heroin.
On the other hand, elements such as cortisol levels or hypothalamus size do not directly induce altered states of consciousness, though they could have indirect effects on the body's stress response or regulatory functions. In the context of altering consciousness, serotonin levels can influence mood and behavioral states, but not in the same direct manner as psychoactive drugs.