a)
- They're definitely one of the best live bands (who are) performing today.
- The two women (who were) sitting next to me were cheering ...
- No one (who was sitting in the arena) seemed to mind.
- Quite a lot of the songs were from their latest album, (which is) currently standing at the top of the charts.
- I'll sit a bit further away from the two women with tuneless voices (who were) trying to sing louder than the lead singer.
The sentences in the review all omit words from the relative clauses.
b)
- who were
- who
- who was
- who is
- that
- that is
- who is
- no deletion possible