The conversion of the english to christianity began a rich period of artistic production in england, especially in the creation of a. secular mosaics. b. illuminated manuscripts. c. ecclesiastical treatises. d. gothic cathedrals.

Could be wrong, so you may want to check this one, but I believe that it is D. because at this time, the Gothic cathedrals were known for there unique artistry, if it is not that then it is A.

The conversion of the English to Christianity began a rich period of artistic production, especially the illustration of manuscripts. Book illustration had not been a very important artistic medium in the Roman world, but because the Christian New Testament was so central to the new faith, the decoration of the Gospels became worthy of the greatest effort.

The above was taken from the text book.

The answer is illuminated manuscripts

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