This makes Niger open to outside attacks.

这使得尼日尔容易受到外界的攻击。

Unlike us, trees don't have blood and bones to protect them from outside attacks, so how exactly does a tree's immune system work?

与我们不同，树木没有血液和骨骼来保护它们免受外界攻击，那么树木的免疫系统究竟是如何工作的呢？

So Poland's greatest geographic challenges to overcome have always been establishing a base on the coast and balancing the area's poorly defensible flat terrain against outside attacks from strong powers in every direction.

因此，波兰需要克服的最大地理挑战一直是沿海岸建立基地，平衡该地区防卫性差的平坦地形，抵御来自各个方向强国的外来攻击。