What was the most important of the reform movements? Explain

What would be considered as the most important reform of the Progressive movement and why?

I have to choose from: 16th, 17th, 18th and 19th amendments and direct primaries, initiatives, referendums or recall.

This is, of course, a matter of opinion. My own view is that, of the reforms listed here, the 19th Amendment is the most important. This is because it did the most to right a wrong and has arguably had the greatest impact on American society.

Most of the reforms that you mention here had the effect of changing relatively minor things about government. The recall, for example, is rarely used.