12. Susan her thesis for two months before her supervisor told her that she was on the wrong path. (work over)

12. Susan had been working over her thesis for two months before her supervisor told her that she was on the wrong path.

Перевод: Сьюзан работала над своей диссертацией в течение двух месяцев, прежде чем ее руководитель сказал ей, что она идет по неверному пути.

Ответ: had been working over