$(a)$ Draw a diagram of the human alimentary canal and label the following: gall bladder, pancreas, liver, and small intestine.
$(b)$ Give two reasons to explain why the absorption of digested food occurs mainly in the small intestine.

(N/A) Refer to the provided diagram of the human alimentary canal.
$(b)$ The absorption of digested food occurs mainly in the small intestine due to the following reasons:
$1$. The inner lining of the small intestine has numerous finger-like projections called $villi$, which increase the surface area for rapid absorption of digested food.
$2$. The $villi$ are richly supplied with blood vessels, which take the absorbed food to each and every cell of the body.