Сделайте следующие предложения вопросительными: he is often sent business abroad. (who? ) these books are sold everywhere. (where? ) professor brown is usually asked a lot of questions after his lecture. (when? ) payment is made against shipping documents. (what? ) tickets for planes are booked in advance. (how? )
Where are these books sold?
?
What is made against shipping documents?
How are booked tickets for planes?