Answer:
Nitrate
Nitrate is the form of nitrogen most used by plants for growth and development. Nitrate is the form that can most easily be lost to groundwater. Ammonium taken in by plants is used directly in proteins. This form is not lost as easily from the soil.
Explanation:
I am not sure if this question means the adjective form or the adjacent form? However, a Schwann cell is a type of glial cell and its main function is to support neurons. Adjacent to the Schwann cell are nodes of Ranvier which are gaps in the myelinated axons, and are believed to assist in potential generation among other things.
I think B seems like the answer.