Not a simple one really, eh?
In simple terms perhaps, the Trailing edge flaps effect is to increase camber and therefore alter lift AND centre of Pressure. In a fixed other variable case, lift increases and CP moves aft. The downwash effect change is seperate and airframe dependent.
Leading edge devices are required because modern Supercritical wings do not respond well to high AoA. Slats act in a similar way to slotted flaps in energising the boundary layer to keep airflow attached at higher AoA, whereas L.E. flaps alter wing shape to alter camber and chord, re-shaping the wing for low speed flight entirely. Some devices function in duel roles, allowing airflow to remain attached at smaller angles of deployment and when fully deployed, reveal a low speed leading edge beneath and function purely as a slat.
To answer the original question, the effect of flap on aircraft attitude is to reduce it at constant airspeed, and if angle of attack is measured from the airframe, then it will reduce. The effective AoA of the wing increases, but providing you qualify your answer, it doesn't matter.
Secondly, slats are there to give the wing a higher AoA ability and do not alter lift significantly in themselves. Different designs will, and some wil lactually create more drag and no lift increase when deployed at the smaller AoA expected at initial flap lever operation.
To answer a tech interview question, as long as you qualify your answers succinctly and without rambling, you can answer several ways. They are looking for a good fundemental knowledge not blind faith in a narrow argument.
This is where multiple choice really falls down, IMHO!