Because the trees were ___,and they couldn't build their nests near our

因为树消失了,他们不能在我家旁边筑巢了.
所以是gone
其实cut我认为也不能算错,因为没有上下文支持
欢迎追问这一段内容是Then people started building houses. They cut down trees, and they filled the field with houses . The robins coud be seen once in a while,然后就是那句了我不知道怎么严丝合缝的解释。写文章的人肯定是想表达消失的意思，可能鸟看到的就是树消失了吧！所以用gone。这样的题不要深究了，明白被动语态的用法就可以了。