Answer:
1. I have never swum in the sea before.
2. It is the most interesting film I have ever seen.
3. She has been learning English for two years.
4. I´m visiting my family next summer.
5. The last time I was in the theatre was two years ago.
Explanation:
To answer this question one must have a good understanding of the present perfect continuous, which is made up of the present perfect of the verb 'to be' (have/has been), and the present participle of the main verb (base+ing).
