The structure of a tooth is given below. What are $P$ and $Q$?

Peyer's patches produce . . . . . . .

The mucosa of the stomach is thick and folded. What are the advantages of this?

$A-$ The permanent teeth begin to replace the temporary ones at about the age of six years.
$R-$ This type of dentition is called diphyodont.

The diagram given below depicts the human digestive system. Label it from $A$ to $F$ and choose the correct option accordingly.

What is the another name of gastro-oesophageal sphincter?