3. Many houses (to build) in our town last year.

3. Many houses (to build) in our town last year.

В данном предложении необходимо употребить глагол «to build» в форме Past Simple Passive.

Past Simple Passive образуется при помощи вспомогательного глагола was/were и третьей формы глагола (Past Participle).

Так как слово «houses» во множественном числе, используем «were».

Третья форма глагола «to build» - built.

Получаем: Many houses were built in our town last year.

Ответ: Many houses were built in our town last year.