求解some of which vs some of them

iclicker

在曼哈顿里Subgroup Modifiers有个例子.

1) Right: This model explains all known subatomic particles, SOME OF WHICH WERE only recently discovered.
为什么这里要加were呢？

SOME OF WHICH only recently discovered.
2) Right: This model explains all known subatomic particles, SOME OF THEM only recently discovered.
为什么1）要加were，2）就不要呢？
不能some of them were...吗？

求各位大神解答。

kluivert

菜鸟来试下：

句子结构不一样
第一句是定语从句，所以要有谓语动词
第二句俺不知道具体叫啥，不过它只是个修饰成分，不可以有谓语动词，否则就是run_on句子了...要么就得加个连词来引导，比如and some of them were...