Why Does Condensation Occur Within a Building

Why does condensation occur within a building?

A) Users leave taps running, baths full, water evaporates and deposits onto room surfaces, making air moist
B) Evaporated water within the building meets surfaces at below dew point temperature
C) Kettles, cooking, fish tanks and open bowls of water evaporate more water vapour into room than ventilation can remove
D) Porous building materials provide pathways for cold moisture to ingress a warm building and make indoor surfaces damp
E) Cyclic variation of indoor surface temperatures always produces below dew point locations