掌握zhǎng wò
to grasp (often fig.), to master提纲tí gāng
the key point, outline提问tí wèn
to question, to quiz, to grill操场cāo chǎng
playground, sports field, drill ground改善gǎi shàn
to make better, to improve改进gǎi jìn
to improve, to make better教材jiào cái
teaching material教训jiào xun
a lesson, a moral, to chide sb