this is one of kaplan
Ionized oxygen is known to contain large numbers of particles X and Y. Repeated lab tests have shown that whenever particles X and Y collide, they produce particle Z. Since the air supply in the offices of the electrical power plant has been shown not to contain any Z at all, it is safe to conclude that that the oxygen in the offices' air supply has not become ionized.
The reasoning above is flawed because the author
A. confuses necessity and sufficiency
B. does not take into account the possibility of improper test conditions
C. relies on the assumption that if a phenomenon can take place, it is bound to take place
D. draws a conclusion despite evidence that is self-contradictory.
E. fails to take into account that other particles can be formed when particles X and Y collide
please explain your choice