3 Tom ..... (recover) in hospital after his fall when he got an invitation to his sister's wedding.

Для выполнения задания необходимо поставить глагол recover в форму Past Continuous.

Past Continuous - Past + to be (was, were) + Ving.

Tom - единственное число, поэтому используем was. Recovering - глагол recover с окончанием -ing.

Tom was recovering in hospital after his fall when he got an invitation to his sister's wedding. (Том выздоравливал в больнице после падения, когда получил приглашение на свадьбу своей сестры).

Ответ: Tom was recovering in hospital after his fall when he got an invitation to his sister's wedding.