Which sentence in the passage uses parallel structure?

a fashion trend not only changes but is also evolving. it grows and is sometimes defining the era in which it originated. in the 1950s, for example, wide-circle skirts and wearing long dresses were in fashion. then in the 1960s, the a-line skirt and a miniskirt became trendy. fashion forecasting involves predicting future trends by observing changes in the current situation and learning from the past trends.