Which rock sub genre first appeared in the 1990s
heavy metal
glam rock
emo
girl bands

Emo is the answer you are looking for 
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Hello!

The Correct Answer indeed would be "Emo" Considering that 

Emo is a style of rock music characterized by melodic musicianship and expressive, often confessional lyrics. It originated in the mid-1980s hardcore punk movement of Washington, D.C., where it was known as "emotional hardcore" or "emocore" and pioneered by bands such as Rites of Spring and Embrace.

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