Answer wouldn’t be B because the Sherman Anti-Trust Act of 1890 forbade any restraint of commerce, which was used against labor unions. However, the Clayton Anti-Trust Act, passed during the progressive era, exempted unions from the Sherman Anti-Trust and stronger enforced the act. The Elkins and Mann-Elkins Acts didn’t really do anything for labor; they just gave the ICC more power to regulate railroads and interstate commerce, along with the Hepburn Act.
In short, best answer would be A.