In HSK 6 grammar, under 词类 → 副词 → 方式副词, the forms include: 不禁、赶忙、特地、特意、偷偷.
不禁
bùjīn
can't help (doing)
赶忙
gǎnmáng
hastily
特地
tèdì
specially; for a special purpose
特意
tèyì
specially; on purpose
偷偷
tōutōu
secretly
暂无。