Which sentence uses commas correctly?
A. Touring Spain, we visited the cities of Madrid, Granada and Seville but we never reached Barcelona.
B. Touring Spain, we visited the cities of Madrid, Granada, and Seville, but we never reached Barcelona.
C. Touring Spain we visited the cities of Madrid, Granada, and Seville, but we never reached Barcelona.
D. Touring Spain we visited the cities of Madrid, Granada, and Seville but we never reached Barcelona.