because 1NT is 15-17 Balanced ; in partner's hands,the cards maybe as these: ♠AXX(X) ♥XXXX ♦A2 ♣AQJ(X) ; ♠ace is sure;or declarer has 6 tricks♥,♦D,♠ace-king; a ♦ return is dangerous; if partner has 4 tricks ♦,then hasnot 15Htcp; so a club return is my choice. if return spade,endplay will be done.