This is an interesting question. I know the OA is A. And we always think B is the right answer.
forbids a strike by the transportation union
Here is something from the dictionary.
forÂ·bid Audio pronunciation of "forbid" ( P ) Pronunciation Key (fr-bd, fÃ´r-)
tr.v. forÂ·bade, (-bd, -bd) or forÂ·bad (-bd) forÂ·bidÂ·den, (-bdn) or forÂ·bid forÂ·bidÂ·ding, forÂ·bids
1. To command (someone) not to do something: I forbid you to go.
2. To command against the doing or use of (something); prohibit: forbid smoking on trains.
3. To have the effect of preventing; preclude: Discretion forbids a reply
If we follows the pattern 3 here, the answer is A.
Note the example..
forbids a reply....forbids a strike..
510 on my first GMAT. 610 on second GMAT.!
The struggle continues.