HSK 7-9
暗中
ànzhōng名
in the dark; in secret; on the sly; surreptitiously
她暗中帮助了不少学生。
Tā àn zhōng bāng zhù le bù shǎo xué shēng.
She secretly helped quite a few students.
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Appears across levels (7-9) in the HSK 3.0 word list.