The condition in which there is a DECREASE in the number of white blood cells in humans is known as: a) leukocytosis (pron: lew-kO-sigh-toe-sis) b) leukopenia (pron: lew-kO-pea-nee-ah) c) leukemia (pron: lew-kee-me-ah) d) leukohyperia (pron: lew-kO-high-per-e-ah)