The "blank check" refers to what policy in the days before world war i? germany's commitment to support austria's attack on serbia. america's promise of aid to great britain. russian willingness to support serbia. germany's commitment to produce as many weapons as required.

The answer is letter b. Germany’s commitment to support Austria’s attack on Serbia. On,  July  5, 1914. Germany gave Austria-Hungary blank check assurance of their unconditional support on whatever plan of action Austria-Hungary will take to punish Serbia, for the reason of Serbia’s assassination of Austria-Hungary’s Archduke and his wife. 

the two atomic bombs dropped on japan in 1945 killed and maimed hundreds of thousands of people, and their effects are still being felt today. the uranium bomb detonated over hiroshima on 6 august 1945 had an explosive yield equal to 15,000 tonnes of tnt.