Explanation:
The alimentary canal or the digestive tract is a long tube that extends from the mouth to the anus. It has four basic layers in its wall, which are:

1. Mucosa: It is the innermost layer of the gut wall, which is in contact with the food. It has three sub-layers:
- Epithelium: It is composed of different types of cells depending upon the location of the gut. For example, in the stomach, it has cells that secrete acid and enzymes, whereas in the small intestine, it has cells that absorb nutrients. It may also have goblet cells that secrete mucus for lubrication.
- Lamina propria: It is a layer of connective tissue that supports the epithelium and contains blood vessels, lymphatic vessels, and immune cells.
- Muscularis mucosae: It is a thin layer of smooth muscle that contracts to change the shape of the epithelium.

2. Submucosa: It is a layer of connective tissue that contains blood vessels, lymphatic vessels, and nerves. It also has glands in some locations, such as the duodenum, which secrete mucus and bicarbonate to neutralize stomach acid.

3. Muscularis externa: It is a layer of smooth muscle that contracts to mix and propel the food along the gut. It has two sub-layers:
- Circular muscle: It contracts to decrease the diameter of the gut lumen.
- Longitudinal muscle: It contracts to shorten the length of the gut.

4. Serosa or adventitia: It is the outermost layer of the gut wall, which is composed of connective tissue and blood vessels. It provides support and protection to the gut.

Now, coming back to the given options, we can see that:

a) Mucosal epithelium has goblet cells which secrete mucus for lubrication: This statement is correct as mentioned above.

b) Mucosa forms gastric glands in the stomach and crypts in between the bases of villi in intestine: This statement is also correct as mentioned above.

c) Cells lining the villi has brush border or microvilli: This statement is correct as the cells lining the villi in the small intestine have microvilli or brush border, which increase their surface area for absorption of nutrients.

d) All the four basic layers in the wall of gut never show modifications in different parts of the alimentary canal: This statement is incorrect as the four basic layers of the gut wall may show modifications in different parts of the alimentary canal depending upon their functions. For example:
- The muscularis externa is thicker in the stomach to churn and mix the food, whereas it is thinner in the small intestine to allow for easier absorption.
- The submucosa has glands in the duodenum to secrete mucus and bicarbonate, whereas it is absent in the ileum.
- The epithelium has different types of cells in different parts of the gut to perform their specific functions.