Which country was the first to declare war in the conflict that would become World War I?

Austria-Hungary

Explanation:

On July 28, 1914, one month to the day after Archduke Franz Ferdinand of Austria and his wife were killed by a Serbian nationalist in Sarajevo, Austria-Hungary declares war on Serbia, effectively beginning the First World War.

Austria-Hungary

Explanation:

Austria-Hungary declared war on Serbia in 1914 after Archduke Franz Ferdinand of Austria and his wife were both killed by a Serbian nationalist.

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c or d both can be the answer