The correct answer is A. isoprene.
Isoprene is a five-carbon hydrocarbon with the chemical formula $C_5H_8$. It is a colorless, flammable liquid that is found in natural rubber and some other plant resins. Isoprene is also produced synthetically and is used to make a variety of products, including rubber, plastics, and pharmaceuticals.
Vinyl chloride is a colorless, flammable gas with the chemical formula $C_2H_3Cl$. It is used to make polyvinyl chloride (PVC), a common plastic. Vinyl chloride is also a known carcinogen.
Acetylene is a colorless, flammable gas with the chemical formula $C_2H_2$. It is used to make a variety of products, including plastics, synthetic fibers, and fuels. Acetylene is also a known carcinogen.
Neoprene is a synthetic rubber that is made from chloroprene. It is a durable, weather-resistant material that is used to make a variety of products, including tires, hoses, and gaskets.
In conclusion, the basic chemical building block of natural rubber obtained from trees is isoprene.