Galileo had not invented the telescope, but on hearing 时态的问题
Galileo had not invented the telescope, but on hearing 时态的问题，请解析，全文如下
Galileo had not invented the telescope, but onhearing, in 1609, that such an optical instrument had been made, he quickly built his own device from an organpipe and spectacle lenses.
这里的时态有什么问题，为什么不应该这样用?
Galileo had not invented the telescope, but onhearing, in 1609, that such an optical instrument had been made, he quickly built his own device from an organpipe and spectacle lenses.
这里的时态有什么问题，为什么不应该这样用?
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