Over the past few decades, the magnetic field has weakened rapidly enough to flip within a few thousand years, but this could also be part of a more limitedvariation.
在过去的几十年里，磁场极速减弱，导致逆转会在几千年内发生，但这也可能只是前奏的一小部分。
2
Variation among humans is limited to the possible permutations of our genes.
人类的变化形式受限于我们基因可能的那些排列。
《柯林斯英汉双解大词典》
3
That does not mean using the same characteristics all over the page but the amount of variation should be limited.