1.(-) This isn't my crayon
    (?) Is this my crayon?
2.(-) Mr.Nam and his wifr aren't engineers
   (?) Are Mr.Nam and his wife engineers?
3.(-) Those aren't bookshelves and books
(?) Are those bookshelves and books?
4.(-) My classroom isn't on the first floor
(?) Is my classroom on the first floor?
5.(-) There aren't 12 students in my class
(?) Are there 12 students in my class?