21) E

Platelets’ role is in blood clotting. Since there is low blood platelet count, blood clotting would be low. 

White blood cells play a role is in disease resistance. Since there a high percentage of white blood cells are abnormal, disease resistance would be low. Note that the question does not say that there is a high percentage of white blood cells. It says that a high percentage of white blood cells are abnormal.

Oxygen transport would be normal as there is nothing mentioned about red blood cells (which carry oxygen) in the question.