In 1996，39 American students started a very interesting project-the Green Tree project．

The students began the project by collecting walnuts（核桃）in autumn．Then the nuts were put under the ground of the school garden in November．In this way，the seeds（種子） could be kept cool and wet for several months before they started growing

In February，the seeds were dug up（挖出）so that they could begin to sprout（發(fā)芽）．Sprouted seeds were kept in refrigerators so that they could be stopped from growing until the time to plant．This helped keep the trees about the same size at planting time．

In March，sprouted seeds were planted in paper cups．Each student was asked to plant twelve trees．Then the trees were carefully watered and watched．The first walnut trees began to appear in about a week．The students found this part of the project very exciting．

On April 29th，the trees were moved and planted by a lake．It took the students only 90 minutes to plant all the trees．It was so interesting to see a treeless area turn into a forest right before their eyes!

1．How did the students begin their Green Tree Project?

2．Why were the nuts put under the ground for several months?

3．When did the seeds begin to sprout?