**Core Concept**
The lacrimal gland secretes tears into the eye through a complex system involving the lacrimal canaliculi, lacrimal sac, and nasolacrimal duct. This system is essential for maintaining ocular surface health and preventing excessive tear flow.

**Why the Correct Answer is Right**
The lacrimal duct, specifically the nasolacrimal duct, opens into the nasal cavity, allowing tears to drain from the eye into the respiratory tract. This opening is crucial for preventing tear overflow and maintaining ocular surface health. The nasolacrimal duct is a muscular tube that connects the lacrimal sac to the nasal cavity, facilitating tear drainage.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a correct location for the lacrimal duct opening. The lacrimal canaliculi, however, do merge to form the common canaliculus that leads to the lacrimal sac.
* **Option B:** This option is not relevant to the lacrimal duct opening. The ciliary body is involved in lens accommodation and aqueous humor production.
* **Option C:** This option is not accurate. The conjunctiva covers the white part of the eye and the inside of the eyelids but is not the correct site for the lacrimal duct opening.

**Clinical Pearl / High-Yield Fact**
The lacrimal duct opening is located in the nasal cavity, specifically in the anteroinferior meatus. This location is essential for understanding lacrimal duct obstruction and its implications for ocular surface health.

**Correct Answer: D. The nasal cavity.**