1. _______ are the main respiratory organs.   Hint First letter clue   2. _______ is a tubular structure through which urine is excreted out of the body.   First letter clue   3. Bronchi are _______ in number.   First letter clue   4. Kidneys are the main _______ organs.   First letter clue   5. Blood is returned to the heart from various body parts through blood vessels known as _______.   First letter clue   6. _______ are the organs of hearing.   First letter clue   7. Blood is distributed to various parts of the body through blood vessels known as _______.   First letter clue