问题描述：
16.__ 1798,when Eli Whitney came up with a new idea,guns had been made by skilled gunsmiths,one at a time.
A to B in
C since D until
再帮我翻译一下,并说明为什么?
A to B in
C since D until
再帮我翻译一下,并说明为什么?
问题解答：
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