Commontale

First, I reviewed the content of each document.
Document 1 mentions that the May Fourth Movement broke out because students protested the decision of the Paris Peace Conference, demanding punishment for the traitors Cao Rulin, Zhang Zongxiang, and Lu Zongyu, and it also describes students storming into Cao Rulin's residence and setting fire to Zhao Family Courtyard.
Document 2 points out that the trigger of the May Fourth Movement was the decision on the Shandong issue at the Paris Peace Conference, which led to student protests.
Document 3 similarly notes that Beijing students opposed the Beiyang government's signing of the Treaty of Versailles and refers to the May 4th assembly and parade.
Document 6 also mentions that the outbreak of the May Fourth Movement was due to China's diplomatic failure at the Paris Peace Conference.
Documents 7 and 10 also state that the decision regarding the Shandong issue at the Paris Peace Conference was the trigger.
Document 19 notes that the direct cause of the student strike was the government's failure to clearly refuse to sign the Treaty of Versailles, which led to the loss of rights in Shandong.
In summary, all the documents point to China's diplomatic failure at the Paris Peace Conference, especially the handling of the Shandong issue—transferring Germany's rights in Shandong to Japan—as the direct trigger that sparked student protests.