The option that revolutionized communication was the model T.
It was Henry Ford -the car genius from Michigan- that invented the Model T, and the affordable automobile to the common citizen. He became so successful with this model. It was first released to the public on October 1, 1908. Its price was $850, a little bit higher for many people but more accessible than other models.
Reason being is that the Tom Thumb is the only invention on the options list that had anything to do with communication. The Cotton Gin, was an agriculture invention, the Model T, was a automobile. And light bulbs, well they are self explanatory.
The Magna Carta in England was a precursor for modern democracy firstly because It took away total control from the monarchy and dispersed it evenly, furthermore, the Magna Carta began to make the ruler responsible under the law. The correct answer is the second option.
The Soviet Union was trying to spread communism all over Korea. The United States joined in with South Korea to fight against the communist North Korea.