【题目】—Why you (look) at the sky?—Because there is a big plane.
【答案】are;looking【解析】句意:—你为什么看天空?—因为有一个大飞机。该句子是现在进行时,其结构是:be+doing,主语you第二人称,因此be动词用are,所以答案是are,looking。