【正确答案】正确答案：Usually, the description of the vowels needs to fulfill four basic requirements: (1) The height of tongue raising (high, mid, low); (2) The position of the highest part of the tongue (front, central, back); (3) The length or tenseness of the vowel (tense vs. lax or long vs. short), and (4) lip-rounding (rounded vs. unrounded).