Complex sentence: Located 14 km from the mainland, it is the largest island in the province which was formerly the island of Hainan which was carved out of Guangdong to became a province in 1988.
Split into simpler sentences: Located 14 km from the mainland, it is the largest island in the province. The largest island formerly was the island of Hainan but that was carved out of Guangdong to became a separate province in 1988.