Which of the Following Is a Characteristic of the Endocardium

Which of the following is a characteristic of the endocardium and why is it important?

A) The endocardium is tough and fibrous, which allows the heart to anchor itself to surrounding structures.
B) The endocardium is thick, which allows the heart to contract forcefully.
C) The endocardium secretes a small amount of serous fluid, which allows the pericardial layers to slide smoothly against one another.
D) The endocardium is smooth, which helps prevent blood clot formation.