Correct answer: A). Soil
The plants obtain nitrogen by the process of absorption from the soil or from the roots in the form of nitrite ions, ammonium or nitrate ions. Plants do not obtain nitrogen from the air, rather it is broken down into nitrogen molecules by the process of nitrogen fixation. The nitrogen-fixing bacteria and archaea live in root nodules of the plant that fix nitrogen in the soil and they have can convert molecular nitrogen from the air into ammonia.
Hence, the correct answer would be option A.
