He was really nice and friendly. He was going to visit his grandmother (27) __ lives in Glasgow. He said he lived there until a few years (28) __ and now he really misses Scotland. I told him (29) __ much I loved his music.

Обоснование:

• (27) Относительное местоимение, которое заменяет существительное 'grandmother' и относится к человеку, — 'who'.
• (28) Оборот, указывающий на прошедшее время и завершение действия, — 'then'.
• (29) Наречие, усиливающее степень выражения, — 'how'.

Ответ: who, then, how