## Core Concept
The phenomenon described, where sensory perceptions cross over (e.g., sounds can be seen and colors can be heard), is known as **synesthesia**. This condition can be induced by certain psychoactive substances.

## Why the Correct Answer is Right
The correct answer, **LSD (Lysergic acid diethylamide)**, is a potent hallucinogenic drug known to cause altered sensory perceptions, including synesthesia. LSD acts on the serotonin system in the brain, specifically as a **5-HT2A receptor agonist**, which leads to its psychoactive effects. This includes alterations in perception, mood, and cognitive processes.

## Why Each Wrong Option is Incorrect
* **Option A:** While cannabis can cause alterations in perception, it is less commonly associated with synesthesia compared to LSD. Its effects are more typically related to euphoria, relaxation, and altered sense of time.
* **Option B:** This option is not specified, but if referring to another drug, there's no direct association mentioned here.
* **Option D:** This option is also not specified, but generally, drugs like opioids or stimulants (if implied) are less likely to cause synesthesia.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **LSD** is a powerful hallucinogen that can induce profound changes in sensory perception, including synesthesia. This effect is a classic association and can be a critical clue in identifying drug use in patients presenting with such symptoms.

## Correct Answer: C. LSD.