Final answer:
The sentence that should be capitalized is: 'The labor unions were fighting for the repeal of the Taft-Hartley Act.'
Step-by-step explanation:
The sentence that should be capitalized is: The labor unions were fighting for the repeal of the Taft-Hartley Act. In this sentence, 'labor unions' is a proper noun and should be capitalized since it refers to a specific group. 'Taft-Hartley Act' is also a proper noun and should be capitalized as it is the name of a specific legislation.
Learn more about capitalization in English sentences