White blood cells, part of the ___________ system, work closely with the ___________ system to protect us from infection and disease.
A) circulatory; immune
B) endocrine; lympathic
C) circulatory; excretory
D) circulatory; respiratory
A) circulatory; immune
B) endocrine; lympathic
C) circulatory; excretory
D) circulatory; respiratory