The letters that most often spell the sound of beginning sun?

The letters that most often spell the sound of the beginning of "sun" are s and sh.

Here's why:

* "S" is the most common spelling for the /s/ sound, and is used in the word "sun" itself.

* "Sh" is also a common spelling for this sound, and can be found in words like "shine," "shadow," and "shook."

While other spellings exist (such as "c" in "cent" or "sci" in "science"), they are less common for this specific sound.