7. While he was writing his famous [текст обрезан] … a) he was worked as a teacher. b) he was work as a teacher. c) he was working as a teacher.

Перевод задания: Пока он писал свою знаменитую [текст обрезан] …

Правильный вариант: c) he was working as a teacher. Оба действия происходили одновременно в прошлом, поэтому используется Past Continuous: was writing и was working.

Пока он писал свою знаменитую [текст обрезан], он работал учителем.