Tense

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X She already closed the door behind her when it occurred to her that she wasn't able to get back in later.
O She had already closed the door behind her when it occurred to her that she wouldn't be able to get back in later.

X The criminal escaped from custody and is believed to flee the country.
O The criminal escaped from custody and is believed to have fled the country.

X some archaeologists believe that the Minoans of 3700 years ago had practiced a religion that involved human sacrifice.
O some archaeologists believe that the Minoans of 3700 years ago practiced a religion that involved human sacrifice.