Planes must zigzag from one ground beacon to the next, and ascend and descend in steps at each stage obtaining permission from the ground.
飞机从一个地面信标到下一个信标曲折飞行,在每一阶段都要经过地面的许可才能上升和下降。
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Either way, if its roots are pulled up from out of the ground as the tree topples over, then there's usually a big hole, a pit left in the ground where the roots used to be.