By Dmitry Antonov and Humeyra Pamuk MOSCOW/WASHINGTON (Reuters) -The United States delivered written replies on Wednesday to sweeping Russian security demands, a key step in a fragile diplomatic process as Russia staged new military drills on land and sea near Ukraine. Secretary of State Antony Blinken said the document, handed over in person by U.S. ambassador to Moscow John Sullivan, addressed Russia’s concerns and raised those of the United States and its allies. He told reporters the response sets out a serious diplomatic path forward, should Russia choose it, and has a principled and prag…