Plzzz
how could the overuse of household disinfectants weaken the immune system?
by killing white blood cells that inhabit the surface of the skin
by breaking down the physical barriers of the skin and mucous
by reducing exposure to pathogens and the creation of specific macrophages
by reducing exposure to pathogens and the creation of specific memory cells

The main way b which household disinfectant harm us is that they kill both good and bad bacteria. When good bacteria are also killed, then chances of the growth of bad bacteria increases. Further, due to over application of disinfectants, chances of development of resistance in the bacteria increases. 
From your choices, it seems B might be the answer, as Disinfectants are chemicals themselves and they cross skin barrier also, so they must be harmful to the mucous and skin barriers of the skin, penetrate deep into the tissue, travel to the other parts and interfere with body systems.