Final answer:
The thalamus is the brain site involved in regulating levels of alertness. It serves as a sensory relay station and is integral to our sleep and wake cycles. The correct option is B.
Step-by-step explanation:
The brain site involved in your level of alertness is the thalamus. The thalamus acts as a gateway for sensory information before it's sent to other areas of the brain for processing. It plays a crucial role in sleep and wakefulness, thus influencing our state of alertness.
The hypothalamus also plays a role in coordinating homeostasis and our body's responses to emotional states, such as the fight-or-flight response. While the amygdala is primarily associated with emotional responses and the hippocampus with memory functions, it is the thalamus that is most directly involved with alertness.