The Blitz:

Within hours of the UK and France declaring war on Germany on 3 September 1939, the RAF bombed German warships along the German coast at Wilhelmshaven. Thereafter bombing operations were against ports and shipping and propaganda leaflet drops. Operations were planned to minimize civilian casualties. From 15 May 1940 – the day after the Luftwaffe destroyed the centre of Rotterdam – the RAF also carried out operations east of the Rhine, attacking industrial and transportation targets. Operations were carried out every night thereafter.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Which two countries declared war on Germany on September 3 1939?
UK and France