Symeon - V04

IMO D (good question). I was b/w C and D

As part of a unified scholarly approach, Symeon, an Eastern Orthodox saint often called “The New Theologian,” collected texts describing existing traditions and relayed them to his readers in a tone of great devotion and authority and borrowing from Asia some aspects of mystical practice.

authority and borrowing from Asia some aspects of mystical practice
authority, and borrowed from Asia some aspects of mystical practice (
authority along with the aspects of mystical practice he borrowed from Asia
authority, borrowing from Asia some aspects of mystical practice
authority borrowing some aspects of mystical practice from parts of Asia

Removign stuff b/w the commas we get:

As part of a unified scholarly approach, Symeon collected texts describing existing traditions and relayed them to his readers in a tone of great devotion and authority........................................

I went with D, beacuse it was the best subordinate clause that fit well into the sentence.