It is a back nasal sound. The pinyin of steam is zheng, and its final is eng, so steam has a back nasal sound. The back-nasal vowels include ang, eng, ing, and ong. The back-nasal vowels all end in g. The pronunciation position is backward, the middle and back part of the tongue is raised, and the tongue base is retracted, resulting in a thick and thick sound. Therefore, words with finals of these four sounds have back nasal sounds.