英音听力讲解:黑客曝光部分美国运动员用禁药

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短语讲解：

1. Russia has accused rebel fighters in Syria of more than 20 violations of the ceasefire so far and called on the US to use its influence to stop them fighting.

so far 迄今为止; 到目前为止
例句：What have you found so far?
你到目前为止发现了什么？

2. New research into mammal reproductions suggests that in principle it might be possible for humans to conceive children without an egg cell.

in principle 原则上，基本上
例句：The present world crisis should in principle be analysed from different temporal perspectives.
原则上说来，目前的世界危机应该从不同的时间角度加以分析。