"These things" most specifically refers to what happened earlier in the chapter. He made His triumphal entry into the city on the back of a donkey, and the people shouted "Hosanna to the Lord!" A great multitude of people wished Him well. From there, He went into the Temple area and overturned the moneychangers' tables and disrupted those who were selling sacrificial animals. This was a direct affront to those who were in charge of the Temple and the Sanhedrin, so their question to Him is: "Who gave You the authority to do these things?"