补充教材404，谢谢！

aiping

406)Many of them chiseled from solid rock centuries ago, the mountainous regions of northern Ethiopia are dotted with hundreds of monasteries.

1)The montainous regions of northern Ethiopia are dotted with hundreds of monasteries, many of which are chiseled from solid rock centuries ago.
2)The montainous regions of northern Ethiopia are dotted with hundreds of monasteries, many of them are chiseled from solid rock centuries ago.

问题：为什么选many of them而不选many of which呢？不太明白

lyricling

本题讨论过。
一是定从简化成分词短语的符合简洁性要求，二是定从中的时态不对。

tocean0222

p.s. The second "are" in chioce 2 should be eliminated in correct answer.