A multigravid client in active labor is about to deliver. The nurse has no help immediately available. What should the nurse do first

A. Prepare a clean area on which to deliver the neonate.
B. Lower the head of the bed to a flat position.
C. Have the client push with a contraction.
D. Ask the client to take a deep breath and hold it.

简述化肥施用对土壤环境的影响？