Why was asoka's rock and pillar edicts written?

The Pillars of Ashoka, the third emperor of the Mauryan dynasty (322-185 B.C.) of India, were erected in Northern India to symbolically reflect both Ashoka's accomplishments as a king and Buddhist doctrine. Ashoka had not embraced Buddhism as a child, only as an adult, and, in spite of his firm belief in that religion, he did not force his subjects to become Buddhists like him. Nevertheless, by erecting this tall and heavy pillars he certainly contributed to spread the message of Buddhism throughout his empire. Some of these pillars, as well as rocks and cave walls located in strategic locations, such as trade routes and pilgrimage sites, have inscribed edicts or proclamations on them, marking the boundaries of his kingdom. Some of them also feature inscriptions that praise the king (his patronage or his generosity and kindness towards his subjects) or ask for forgiveness for the massacres committed.    

the navigation act prevented the colonies from exporting to countries other than britain and it prevented the importation of goods by other countries as well. so i believe the correct answer is d. other nations could not deliver goods to the colonies.

hope this .