Complex sentence: Since 1900, Narón has been growing non-stop, reaching its highest level during the 1960s and the 1970s, coinciding with the period of development of the naval industry of Ferrol and Fene.
Split into simpler sentences: Since 1900, Narón has been growing steadily, reaching its highest level during the 1960s and the 1970s. This period of growth coincided with the period of development of the naval industry of Ferrol and Fene.