一道sat语法(IE)英语问题

题目

一道sat语法(IE)英语问题
a great gray owl flying low across a forest clearing , its wings beating quietly and its ultrasensitive ears tuned to the faint sounds that ……
答案是在“flying 前面加was” ，这我明白，可是为什么后面是beating？按理说后面有and，beating应该和tuned一致才对啊？

答案

and 连接两个 独立主格结构
its wings beating 和its ultrasensitive ears tuned to the faint sounds
beating和tuned 主要看和前面wings和ears的关系.主动用doing,被动用done
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