Which sentence most effectively uses a formal style and tone?

The process of redefining the British political nation seemed like it got dragged out forever, beginning in the 1820s and going into the 1900s.

I cannot believe that by the 1880s, no women and only 60 percent of the male population had the right to vote in England.

It is preposterous and shameful that only 60 percent of men, and no women at all, had the right to vote in Britain in the 1880s.

The campaign for women's suffrage began in the 1830s, but it was not until the start of the 20th century that the movement truly took hold.

The answer to your question would be that the sentence that uses a formal style and tone most effectively is the following one: The campaign for women's suffrage began in the 1830s, but it was not until the start of the 20th century that the movement truly took hold.

This is the case because the sentence is a fact without any kind of subjective opinions (such as the second and third options: "I cannot believe", "it is preposterous and shameful") and it does not use a talkative oral style (such as the first option: "the process of redefining the British political nation seemed like it got dragged out).

The campaign for women's suffrage began in the 1830s, but it was not until the start of the 20th century that the movement truly took hold. Sounds more formal because it doesn't include a opinion and it doesn't include words that weren't cited from people there in that time.