The vowel letter u is pronounced short in stressed closed syllables? /,when pronounced, the tip of the tongue is far away from the lower teeth, the middle part of the tongue is raised, and the tongue position is between the low position and the middle and low position, which is the lowest among the three vowels, and the gum is between half-open and open, which is the largest among the three vowels. Lips are flat and usually appear in the position of prefixes and words, such as:

Sun Sun (the central celestial body of the solar system)

Umbrella

bus

Nut walnut

Gungun

Uncle, uncle, uncle, uncle.

Under is under (directly below).

I hope it can help you solve the problem.