Read this: Within the Luftwaffe, there was a more muted view of strategic bombing. The OKL did not oppose the strategic bombardment of enemy industries and or cities, and believed it could greatly affect the balance of power on the battlefield in Germany's favour by disrupting production and damaging civilian morale, but they did not believe that air power alone could be decisive. Contrary to popular belief, the Luftwaffe did not have a systematic policy of what became known as "terror bombing". Evidence suggests that the Luftwaffe did not adopt an official bombing policy in which civilians became the primary target until 1942.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What year did the terror bombing policy become official?
1942