_______ regulates the opening of oesophagus into the stomach. The opening of the stomach into the duodenum is guarded by ________ .

Question

( A ) A fold of mucous membrane, the pyloric sphincter
( B ) Gastro-oesophageal sphincter, the pyloric sphincter
( C ) A fold of mucous membrane, muscular sphincter
( D ) Muscular sphincter, a fold of mucous membrane