短语讲解：

1. Before the miners began working in the caves, the area was isolated from the surface and the outside world.

be isolated from 绝缘
例句：Patients will be isolated from other people for between three days and one month after treatment
治疗结束后，病人将与其他人隔离3天到1个月的时间。

2. Boston said the researchers could only work for about 20 minutes at a time before they had to go to a room that was 38 degrees Celsius to cool down.

at a time 依次， 逐一， 每次
例句：Can I borrow two books at a time ?
我能一次借两本书吗？

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