The thick middle, muscular layer of the heart is the a. endocardium b. myocardium c. tricardium d. pericardium

When you improve the ability of your muscles to repeatedly exert themselves you're improving your

How do the uv rays cause damage?   what exactly causes the skin to burn;   can you be more specific about this mechanism?   3. how do photosensitive medications increase a person's sensitivity to sunlight and therefore increase their risk of getting burned?     what kind of medications can increase photo-sensitivity, can you think of some examples?

So i have a lot of answers answered but it says i still need to answer more questions. why is it doing that? how many questions need to be answered?