HSK 3
Tā cóngxiǎo jiù bǐjiào píngxiōng.
She's been pretty flat-chested since she was little.
HSK 4
Píngxiōng nǚhái chuān zhèzhǒng yīfu fǎn'ér hǎokàn.
This kind of clothing actually looks better on flat-chested girls.
HSK 7-9
Wǎngshàng yǒu bùshǎo jiēshòu zìjǐ píngxiōng de bózhǔ.
There are many bloggers online who embrace being flat-chested.