**Core Concept**
The development of the paranasal sinuses is a complex process that involves the formation and expansion of air-filled cavities within the bones of the skull. The development of the sinuses is closely tied to the growth and development of the face and skull.

**Why the Correct Answer is Right**
The maxillary sinus is the first paranasal sinus to develop, and it develops from the maxillary antrum, which is a cavity within the maxilla bone. The maxillary sinus develops from the first pair of pharyngeal arches and begins to form around the 12th week of gestation. The maxillary sinus is the largest of the paranasal sinuses and plays a crucial role in the drainage of the nasal cavity.

**Why Each Wrong Option is Incorrect**
**Option A:** The frontal sinus is the last paranasal sinus to develop, and it begins to form around the 6th year of life.
**Option B:** The sphenoid sinus develops later than the maxillary sinus, around the 2nd year of life.
**Option C:** The ethmoid sinus is composed of multiple small air cells and develops from the ethmoid bone, but it is not the first paranasal sinus to develop.

**Clinical Pearl / High-Yield Fact**
The development of the paranasal sinuses is closely tied to the growth and development of the face and skull, and abnormalities in sinus development can lead to a range of clinical problems, including sinusitis and nasal obstruction.

**Correct Answer: A. Maxillary sinus.**