How do girls' breasts develop during puberty?

Women's breasts come in many different shapes and sizes. When entering puberty in girls, from a "flat" chest, girls' breasts will gradually grow larger and become "double mountains". So how do girls' breasts develop during puberty and what should be noted?

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When breasts first start to grow, no one talks about it. There aren’t any greetings cards that say, ‘Woo Hoo! Your breasts are developing!’ but you

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