Explanation:

The Gurumukhi script was standardized and popularized by Guru Angad Dev (Option C), the second of the ten Sikh Gurus. He refined the existing Punjabi script to make it suitable for writing the Sikh scriptures, including the teachings of Guru Nanak Dev (Option D), the founder of Sikhism. Guru Amardas (Option A) and Guru Ramdas (Option B) were subsequent Gurus who contributed significantly to Sikhism but did not introduce the script.