遗憾的是,很遗憾
it是形式主语,真正的主语是that后的一长串
It is sad that it can't be built.很遗憾,它无法建造
It is sad that we cannot celebrate it as such.很遗憾,我们不能这样庆祝。
It is sad that some hotels choose to discriminate.令人遗憾的是,一些酒店选择歧视。
It is sad that this may have changed.令人遗憾的是,这种情况可能已经改变。