a)
The purpose of the festival is to raise money for Amnesty International.
b)
- e
- c
- d
- a
- b
c)
The first line is too formal. It would be better to use an informal expression like Come to / Come and enjoy this year's Freedom Festival. Also, the paragraph does not sound enthusiastic enough: the word nice in 'a nice event' is weak, as is the word good in 'a good cause'. There is an unnecessary passive ('we are sure the event will be enjoyed') where an active would be better ('we know you will enjoy this exciting event').