Explanation
$$\textbf{Correct answer: D}$$
$$\textbf{Option (A):}$$
$$\bullet$$ There is the presence of saliva in the mouth which contains salivary amylase. It is responsible for digesting the boiled starch which is converted to maltose.
$$\bullet$$ In the mouth, there is the absorption of drugs which induces fast activity. This type of cell is not present in the mouth
$$\textbf{Option (B):}$$
$$\bullet$$ The stomach is the region starting the highest level of digestion in the alimentary canal.
$$\bullet$$ The process of digestion by gastric enzymes occurs in this region. This makes it easier for the food to be absorbed.
$$\textbf{Option (C):}$$
$$\bullet$$ Small intestine has the highest level of absorption.
$$\bullet$$ This is the region where most nutrients are absorbed, but the molecules previously digested by the system do not reach the intestine for absorption.
$$\textbf{Option (D):}$$
$$\bullet$$ The absorption of nutrients and drugs takes place throughout the alimentary canal. This means in the different regions of the alimentary canal the absorption of nutrients takes place.
Hence, the correct answer is option (D).
$$\textbf{Correct answer: A}$$
$$\bullet$$ Saliva is secreted in the mouth cavity from the salivary glands. There is salivary amylase present which helps in the digestion of starch.
$$\bullet$$ About 30% of the starch digestion occurs in the mouth with the help of salivary amylase.
$$\bullet$$ So, the mouth cavity is responsible for starting carbohydrate digestion.
$$\bullet$$ Small intestine is the region in which digestion of all the nutrients takes place.
$$\bullet$$ This is because of the presence of pancreatic juice and the intestinal juice that contains the different enzymes for digestion.
$$\bullet$$ But water absorption takes place in the large intestine.
$$\bullet$$ The pancreas is the region for the secretion of pancreatic juice containing different enzymes.
$$\bullet$$ Pancreatic juice also contains pancreatic lipase which helps with the digestion of fat in the small intestine.
$$\bullet$$ The pancreas is not the site for digestion as all the enzymes are released into the duodenum.
$$\bullet$$ Liver is responsible for the secretion of bile.
$$\bullet$$ This helps with the emulsification of fat and facilitates the absorption of fat. Therefore the liver is not responsible for protein digestion in the system.
Hence, the correct answer is option (A).
$$\textbf{Option (A) and (C):}$$
$$\bullet$$ The duct which is labelled as 'A' is called the hepatopancreatic duct.
$$\bullet$$ The secretion of bile from the liver is possible with the hepatic duct from the liver.
$$\bullet$$ The concentrated bile juice contains bile pigments and bile juice is secreted from the liver and is stored in the gall bladder.
$$\bullet$$ If the hepatopancreatic duct is blocked in the pancreatic juice containing the pancreatic enzymes and bile juice.
$$\bullet$$ The pancreatic juice contains pancreatic amylase which facilities the digestion of carbohydrates.
$$\bullet$$ The pancreatic juice contains trypsinogen which gets activated to trypsin. Trypsin is responsible for the digestion of proteins.
$$\bullet$$ The pancreatic juice contains pancreatic lipase and along with it, bile pigment is responsible for the proper digestion of fats.
$$\bullet$$ Digestion of all carbohydrates, proteins and fats is affected when the hepatopancreatic duct is blocked.
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