Teacher:In this task, a passage will be given and the goal is to generate a question about temporal relations based on that passage. A temporal relation describes the relation between two things with respect to time e.g., something happens/starts/terminates/... immediately/shortly/usually/... before/after/during/... something else.
 Your question should include an event, or ask about an event, and should not be a yes/no question.
Teacher: Now, understand the problem? Solve this instance: Passage: Meanwhile, precipitation in the central part of northwest China, the southwestern part of the Qinghai-Tibet plateau and most stretches of central and north China tended to decrease obviously. Zuo Hongchao, who took part in the precipitation investigation, said the research was of great importance, as changes in precipitation would impact water resources, agricultural production and the ecological system in China.
Student:
What event has already finished?