【阅读选择】Climate scientists are not present everywhere. Because there are so many places in the world and not enough scientists to observe all of them, they're asking for your help in observing signs of climate change across the world. The citizen scientist movement encourages ordinary people to observe a very specific research interest—birds, trees, flowers budding, etc, and send their observations to a giant database to be observed by professional scientists. This helps a small number of scientists track a large amount of data that they would never be able to gather on their own. Much like citizen journalists helping large publications cover a hyper-local beat, citizen scientists are ready for the conditions where they live. All that's needed to become one is a few minutes each day or each week to gather data and send it in. In “All that's needed to become one... (paragraph 2) ”, what does the word “one” stands for ?