The correct answer is option 'D' - thalamus.

Explanation:
The apple and pear are fruits of the Rosaceae family. In these fruits, the edible part is not the outermost layer (epicarp), middle layer (mesocarp), or innermost layer (endocarp), but rather the swollen base of the flower known as the thalamus or receptacle.

1. Epicarp:
- The epicarp is the outermost layer of the fruit, also known as the skin or peel.
- It is mainly composed of cuticle, which protects the fruit from external factors like pathogens and dehydration.

2. Mesocarp:
- The mesocarp is the middle layer of the fruit.
- In apples and pears, the mesocarp is fleshy and forms the majority of the fruit's volume.
- It is responsible for providing the fruit with its characteristic texture and juiciness.

3. Endocarp:
- The endocarp is the innermost layer of the fruit.
- It can be hard or stony, as seen in fruits like peaches or plums.
- In apples and pears, the endocarp is thin and not typically consumed.

4. Thalamus (Receptacle):
- The thalamus, also known as the receptacle, is the swollen base of the flower from which the fruit develops.
- In apples and pears, the thalamus becomes fleshy and forms the edible part of the fruit.
- It is the part of the fruit that surrounds the seeds and provides a sweet and juicy taste.

In conclusion, the edible part of an apple and pear is the thalamus or receptacle, which forms the fleshy, sweet, and juicy portion of the fruit.