Complex sentence: The Ilocos Region occupies the narrow plain between the Cordillera Central mountain range and the South China Sea, and the northern portion of the Central Luzon plain, to the north-east of the Zambales Mountains.
Split into simpler sentences: The Ilocos Region occupies the narrow plain between the Cordillera Central mountain range and the South China Sea. It also occupies the northern portion of the Central Luzon plain, to the north-east of the Zambales Mountains.