If you were looking at a organ composed of billions of nerve cells what would it be a)heart b)lungs c)pancreas d)brain

The Brain is a complex organ composed almost entirely of nervous tissue, that is compacted and folded up. These nervous tissue pass electrical signals that form complex processes that not only control all other organs, but also give us feeling and thought.

If you were looking at a organ composed of billions of nerve cells what would it be?

I think its D brain because The nervous system takes in information through our senses, processes the information and triggers reactions, such as making your muscles move or causing you to feel pain.

Example: For example, if you touch a hot plate, you reflexively pull back your hand and your nerves simultaneously send pain signals to your brain. 

Osteocytes for me is the portion of the

Subtract your 2-minute  heart rate  from the  heart rate you took immediately after exercising. the faster your heart rate  recovers the fitter and healthier your  heart.