Ответ:

1) The weather was very frosty last December.

2) The film was not(wasn't) very interesting.

3) Ben and his parents were at the ski resort.

4) The businessmen are(were) in the meeting room.(По Вашему усмотрению, они могут быть или сейчас(are) или они были(were)

5) Our teacher was very tired yesterday.