6 They started working at the bookshop when they were eighteen. They _________ _________ at the bookshop _________ they were eighteen.

6 They started working at the bookshop when they were eighteen.

They _________ _________ at the bookshop _________ they were eighteen.

В данном предложении необходимо использовать Present Perfect, чтобы показать, что действие началось в прошлом и продолжается до настоящего времени. Предлог "since" используется, когда указывается конкретная точка во времени (в данном случае, they were eighteen).

Слова, которые нужно вставить: have worked, since

Предложение полностью: They have worked at the bookshop since they were eighteen.

Ответ: They have worked at the bookshop since they were eighteen.