尽管他不是最优秀的歌手，但他的舞台魅力有着独特的x因素。

Though not the best singer, his stage presence has that distinctive ___x-factor.

她的魅力有一种难以言说的特质，那就是成功的x-factor。

Her charm has an indescribable quality that is the ___x-factor for success.