https://phys.org/news/2018-05-facebook-chief-eu-grilling-digital.html

After short opening remarks, Zuckerberg listened to all the questions first, and then responded to them all at once. There was no back-and-forth with lawmakers, as happened during his testimony in front of the U.S. Congress last month.

As a result, he was able to avoid giving some answers and ran out of time to provide others.