Ответ:

1.1 Who were reading a book when I came?

1.2 what were they doing when I came?

1.3 They were reading a book when I came, weren't they?

1.4 were they reading a book or a magazine when I came?

1.5 were they reading a book when I came?

2.1 What she did last week?

2.2 Who sang a nice song last week?

2.3 She sang a nice song last week, didn't she?

2.4 She sang a nice song last week or last month?

2.5 did she sing a nice song last week?