The correct options are
B There is momentary lowering of the pressure in the proximal region of the stomach to hold more volume of bolus.
C When bolus is inside the stomach, the lower esophagial spincter contracts to prevent the backward movement of the bolus towards the oesophagus.
D Gastric reflux happens when gastric juice tends to move upwards towards the lower pressure region in oesophagus and is prevented by cardiac sphincter.
The first option is incorrect because the abdominal pressure is higher than the oesophageal pressure. The bolus still enters the stomach due to the momentary lowering of the pressure in the proximal region of the stomach and this phenomenon is known as receptive relaxation. Hence, the bolus slides down into the stomach easily.