试试 HanyuGuide 的主动间隔重复系统。
开始 7 天免费试用 · US$49.99 / 年
to use
difficult (to...)
disaster
hard to (predict, imagine etc)
Qi son of Yu the Great 禹[yǔ], reported founder of the Xia Dynasty 夏朝[xià cháo] (c. 2070-c. 1600 BC)
to open one's mouth
tooth