Stuck on last three. Any help please.
3d Holiday? You don't say! (7) -e-a-a-
17d Excitement of a bet (7) -l-t-e-
21d Listen to river flowing back under hospital(4) h-e-
Also, can anyone give me the reason why 20a is CACHALOT? I get 'cach' -endless supply-ie miss off the 'e' and 'a lot' as 'plenty' but what is the whale reference?