Definition: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: Mountaineers have noted that as they climb, for example, up to the 12,633foot Humphreys Peak in Arizona, plant life changes greatly. In the Sonoran Desert, one climbs into a pine forest at 7,000 feet and a treeless tundra  on the top of the mountain. It may seem that plants at a given altitude are associated in what can be called "communities" -groupings of species. The idea is that over time, plants that require particular climate and soil conditions come to live in the same places, and are frequently to be found together. Scientists study the history of plant life and build up a picture of how groups of plants have responded to climate changes and how ecosystems develop. But are these associations, _ are real in the present, permanent? A great natural experiment took place on this planet between 25,000 and 10,000 years ago, when small changes in the earth's orbit caused great sheets of ice to spread from poles. These glaciers  covered much of North America and Europe to depths of up to two miles, and then, as the climate warmed, they retreated. During this retreat, they left behind newly uncovered land for living things to occupy, and as those living things moved in they laid down a record we can read now. As the ice retreated and plants started to grow near a lake, they release pollen . Some would fall into the lake, sink to the bottom and mix with the sand. By drilling into the lake bottom it is possible to read the record of the plant life around the lake. The fossil record seems clear; there is little or no evidence that entire groups of plants moved north together. Things that lived together in the past don't live together now, and things that live together now didn't live together in the past. Each individual living things moved at its own pace. The fossil record seems to be telling us that we should be thinking about preserving species by giving them room to move about-to respond to environmental changes. 
 Answer: depends upon climate and soil conditions
