406. Many of them chiseled from solid rock centuries ago,the moutainous regions of northern Ethiopia are dotted with hundreds of monasteries. A...... B...... C...... D.The moutainous regions of northern Ethiopia are dotted with hundreds of monasteries, Many of which are chiseled from solid rock centuries ago. E.The moutainous regions of northern Ethiopia are dotted with hundreds of monasteries, Many of them chiseled from solid rock centuries ago.
The "which" in D can refer to either regions or monasteries, thus causing ambiguity. But choice E,by using an apposotive led by "them", avoids such a problem and becomes more concise.