Are. потому что в предложение множественное число
1. Jane supposed they would go to the theatre the following day.
Strong-stronger-the strongest
big-bigger-the biggest
pretty-prettier-the prettiest
slowly-slowlier-the slowliest
helpful-more helpful-the most helpful
badly-worse-the worst
little-less-the least
good-looking-better-looking-the best-looking
simple-simplier-the simpliest
expensive-more expensive-the most expensive
1-е предложение-any
2-e предложение-a
3-e предложение-аny
4-e предложение-a
5-e предложение-some
6-e предложение-а
7-е предложение-а