FBR$,$ Inc. and NBAC are in the same industry, but FBR$,$ Inc. is unionized and NBAC is not. Therefore,

Question $11$ options:

it can be argued with assurance that any wage differences between the two firms are due to the presence of a union in FBR$,$ Inc. and the absence of a union in NBAC.

it is difficult to argue with assurance that wage differences between the two firms are attributable to the presence of a union, although the possibility exists.

any wage differences between the two firms can never be attributed to the presence of a union in FBR$,$ Inc.

NBAC has to form a union to compete with FBR$,$ Inc.