Final answer:
a) Endocardium. The membrane that lines the heart and forms the valve flaps is called the endocardium. It covers the heart chambers and valves and is made up of simple squamous epithelium.
Step-by-step explanation:
The membrane that lines the heart and forms the valve flaps is called the endocardium. It is the innermost layer of the heart wall and covers the heart chambers and valves. The endocardium is made up of simple squamous epithelium called endothelium, which is continuous with the endothelial lining of the blood vessels.