**Explanation:**

The earthworm has a well-developed excretory system consisting of nephridia. Nephridia are specialized tubular structures that function in excretion and osmoregulation. In earthworms, there are three types of nephridia: septal nephridia, integumentary nephridia, and pharyngeal nephridia.

The enteronephric nephridia, also known as intestinal nephridia, are a type of septal nephridia. They are located in the posterior region of the body, near the intestine. These nephridia open into the intestine and are responsible for excreting metabolic waste and maintaining the osmotic balance in the earthworm.

**Reasoning:**

1. **Septal Nephridia in Earthworm:** Septal nephridia are specialized excretory organs found in each segment of the earthworm's body. They are connected to the coelomic cavity by a funnel-shaped structure called a nephrostome.
2. **Location of Enteronephric Nephridia:** Enteronephric nephridia are a type of septal nephridia that are located in the posterior segments of the earthworm's body, near the intestine.
3. **Function of Enteronephric Nephridia:** Enteronephric nephridia are responsible for excreting metabolic waste and maintaining the osmotic balance in the earthworm. They collect waste materials from the coelomic fluid and transport them to the intestine for elimination.
4. **Opening of Enteronephric Nephridia:** The enteronephric nephridia open directly into the intestine of the earthworm. This allows the waste products to be eliminated from the body through the digestive system.
5. **Options Provided in the Question:**
a) Body surface: This is incorrect as enteronephric nephridia open into the intestine, not on the body surface.
b) Buccal cavity: This is incorrect as enteronephric nephridia open into the intestine, not into the buccal cavity.
c) Intestine: This is correct as enteronephric nephridia open directly into the intestine.
d) Both 2 & 3: This is correct as enteronephric nephridia open into the intestine, which is option 3, and not on the body surface or buccal cavity, which are options 1 and 2 respectively.

Therefore, the correct answer is option 'D' - Both 2 & 3, as the enteronephric nephridia open into the intestine of the earthworm.

The pharyngeal nephridia of 6th segment open into the buccal cavity in 2nd segment while those pharyngeal nephridia of 4th and 5th segment open into the pharynx(anterior region of alimentary canal).. and the septal nephridia open into the intestine..