13a Please register volunteers at home (9) E_T_R_ _ _ _
16d Trick one student to take cat round America (8) _L _ _ _ _ _ _
17d Fetch back dog without a tail (8) _E_ _ _ _ _ _
17d Retrieve - I understand why, as for 13a Entertain and 17d Illusion - can anyone enlighten me as to why? would be very grateful if you could, still cant work them out why these are the answers and i hate it when a crossword gets the better of me.