The structure in earthworm which serves as a wedge to force open cracks in the soil is
(a) Peristomium
(b) Setae
(C) Clitellum
(d) Typhlosole
(e) Prostomium

Hint: Earthworms have a long and cylindrical body of length between 15- 20cms. There is a structure in the anterior part of the worm that helps them to make burrows in the soil.

Complete answer:
The prostomium is a small fleshy lobe like structure that overhangs the mouth of the earthworm or acts as a covering for the mouth and its main function is to serve as a wedge to force open cracks in the soil into which the earthworm may crawl in or live.
- There are 100 - 120 segments present in the body of an earthworm.
 - Peristomium is the first body segment of earthworm. It carries the mouth.
- Setae are bristles like structure that help in anchoring the soil for movement.
- The clitellum is formed by the fusion of six segments i.e., from segments 32 to 37. It produces cocoons to enclose the eggs of the earthworm.
- Typhlosole is the internal folding of the wall of the intestine to increase the area of absorption of digested food.
So, the correct answer is, ‘prostomium’.

Note: In earthworms, the nose, eyes, ears, or hands were not present. Their function is carried out by Prostomium so it also serves as a sensory device to gather sensory information regarding their environment. They are found all over the world where the condition of soil, temperature, and water are favourable. They make a tunnel through the ground, by eating their way through the soil. In this way they also drag leaves and other shredded parts of plant down into the soil, this tunnel or hole allows air to enter the soil and water to drain through. This activity makes or converts the dense infertile soil into rich fertile soil.