Final answer:
The sentence 'Mandatory labeling of genetically engineered foods in the United States has been proposed by several congressional bills' is in passive voice.
Step-by-step explanation:
The sentence 'Mandatory labeling of genetically engineered foods in the United States has been proposed by several congressional bills' is in passive voice.
In passive voice, the subject of the sentence receives the action performed by the verb. Here, the subject (mandatory labeling) is not performing the action of proposing, but rather is receiving the action. The verb 'has been proposed' is in the past participle form to indicate the passive voice.
In contrast, the sentence 'Several congressional bills have proposed mandatory labeling of genetically engineered foods in the United States' is in active voice, where the subject (several congressional bills) is performing the action of proposing.
Learn more about Active and Passive Voice