Question on developmental biology?

If referring to a human embryo...

E. Septum transversum.

Explanation: The septum transversum is very important in embryologic development because it aids in separating the parietal and pericardial cavities from the abdominal cavity... so it's basically the primitive diaphragm. During fetal development it becomes the central tendon of the diaphragm and if you look at an image of a developed pericardial sac, you will see that inferior portion of the fibrous pericardium is attached to the central tendon (the remnants of the septum transversum).

Great question! Really work on being able to visualize how things develop during this stage of embryologic development because it will help you once you're in fetal development (weeks 9-40) and in gross anatomy.