What is the sentence of sound so wistful?

The sentence "sound so wistful" isn't a complete sentence on its own. It's a phrase that describes a sound. To make it a complete sentence, you need to add a subject and a verb. Here are a few examples:

* The music sounded so wistful.

* Her voice sounded so wistful as she spoke of her childhood.

* The wind whistling through the trees sounded so wistful.

The phrase "sound so wistful" can be used to describe a variety of sounds, including music, voices, and natural sounds. It implies a sense of longing, sadness, or nostalgia.