Complex sentence: Attachment theory was extended to adult romantic relationships in the late 1980s by Cindy Hazan and Phillip Shaver, who proposed and identified four styles of attachment: secure, anxious-preoccupied, dismissive-avoidant and fearful-avoidant.
Split into simpler sentences: Attachment theory was extended to adult romantic relationships in the late 1980s by Cindy Hazan and Phillip Shaver. Four styles of attachment have been identified in adults: secure, anxious-preoccupied, dismissive-avoidant and fearful-avoidant.