Can someone please help me answer this I suck at biology

What protects the lining of the stomach from acidic gastric juices?

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Click an item in the list or group of pictures at the bottom of the problem and, holding the button down, drag it into the correct position in the answer box. release your mouse button when the item is place. if you change your mind, drag the item to the trashcan. click the trashcan to clear all your answers. label the following topographic map. click on a label below the map to select it, and then click on the appropriate box on the map to place the label. (increments for contour lines is 50 ft).