One of the Symptoms of Kidney Disease Is the Presence

One of the symptoms of kidney disease is the presence of proteins in a patient's urine. To quickly test for kidney disease using a urine sample, a doctor might add a chemical that causes a color change when

A) nitrogen, but not oxygen, is present.
B) nitrogen, but not phosphorus, is present.
C) only oxygen and hydrogen are present.
D) only carbon and hydrogen are present.