What is the key to effective communication?

Speaking clearly, letting the person know excastly what you are thinking/feeling

You answer would be c.

Of that are from eating black  foods or iron supplements. the most common condition causing  it is a bleeding ulcer.  black poop caused by blood indicate a problem in the upper digestive tract.     along with pain, vomiting, or diarrhea is cause to see a doctor right go see a doctor