Possibilities are like the wings of birds; they allow man to soar and to climb to the heavens. And facts are like the atmosphere                  those wings must beat, and without which the soaring bird will surely plummet back to earth.

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so that

in case

against which

考查定语从句。句意：可能性就像鸟儿的翅膀；它们让人类翱翔，爬向天堂。事实就像空气，翅膀必须与之对抗，没有它，翱翔的鸟儿肯定会坠落到地面。空处引导定语从句，先行词是atmosphere，从句结构完整，应用关系副词或者介词 + which引导，此处是固定搭配：beat against意为 “撞击”，用against which引导。故选D。