Answer:
Mast cells are a type of white blood cells that is found in connective tissues all through the body, especially under the skin, near blood vessels and lymph vessels, in nerves, and in the lungs and intestines.
Oxygen is the by-product or waste product of photosynthesis. Plants do not make oxygen just for us.
Rachel Carson's warning in silent spring was focused on : The misuse of pesticide
The book was published in 1962 and documented the effect of the use of pesticide to the environment
hope this helps