1、Why does this happen?
2、How could this be?
3、How can it be?
4、how did we come to this?
为什么：why; why is it that; how is it that; forwhy; whereto
出现：appear; appearance; arise; emerge; grow
现象：phenomenon; appearance
例句：
1、为什么会出现这种现象呢？在大量的实验中，我们发现各种材料中均有价电子密度以及正电子寿命饱和的现象，但目前还没有人深入研究这种现象的本质。
Over a very large number of experiments, we found that the phenomenon of covalence density and positron life saturation are almost existed in all kinds of materials, but there is still no one in-depth study on the nature of this phenomenon.
2、为什么会出现上述这种相反的现象呢？
Why does this reverse phenomenon appear?
“为什么会出现这种现象”翻译成英文：
Why will appear this kind of phenomenon
内容如下：why did it happen?或者How could this be?