Explanation:

The priority nursing care during the post-op period for a client who underwent an abdominal perineal resection is to facilitate perineal wound drainage. This is crucial for preventing infection of the surgical site and promoting healing. Teaching perineal wound care techniques, as in choice A, is more appropriate than ileostomy care in this scenario. While monitoring electrolyte levels is important, it is not the priority compared to ensuring proper wound drainage, making choice B less crucial. Encouraging early ambulation, as in choice C, is beneficial but not as critical as facilitating wound drainage immediately post-op.