"Have you ever seen a blue bird?"
Is there any difference between 蓝鸟 and 蓝色的鸟。 is seems they are used arbitrarily by Duolingo with the other being wrong although I see no difference in the usage.
However， 蓝色的鸟is better。 类似蓝鸟这种较为简略的称呼形式，更适合用于生活中常见的事物，比如黄猫，黑狗。 此外，蓝鸟也可以是专有名词，比如某款轿车就叫蓝鸟。
泛指不加数量词，just like the differece between"there is a bird"and"there are birds".
看不等于看见。看更接近look，强调外在动作；见更接近see，强调内在结果。这里应该用见过，你见过蓝色的鸟吗？ 看过也不是完全不能用，比如讨论看电影，就可以说，你看过某个电影吗？因为看电影描述的是看的过程，一个活动，无需关注内在结果。瞎子也不会看电影，对不对？ 总之，this translation is somehow inappropriate. How could I report it to Duo's Chinese team？
If I wanted to used the "看不看" form here, what would the word order be? I took a wild guess at "你看不看过..." but I'm not sure where the aspect particle should go. Not that Duolingo accepts anything but the "...吗?" form, anyway...