Statement that that explains the effects that can be felt in immune system by stress is A: Stress can lead to increased vulnerability to infections and immune deficiency disorders.
Stress can be regarded as any tension to our body, this could be emotional or physical and this is not good for our well being and our health generally.
When there so much stress, it can affect our immune system which is the system that provide resistance to infection and toxins and once this system is weak we will be vulnerable to infections.
Therefore, option A is correct.