this; these; (commonly pronounced zhei4 before a classifier, esp. in Beijing)[cedict]
道
dàoㄉㄠˋ
direction; way; method; road; path; classifier for long thin stretches, rivers, roads etc; principle; truth; morality; reason; skill; method; Dao (of Daoism); to say; to speak; to talk[cedict]
難題
nán tíㄋㄢˊ ㄊㄧˊ
difficult problem[cedict]
還
háiㄏㄞˊ
huánㄏㄨㄢˊ
also; in addition; more; still; else; still; yet; (not) yet[cedict]
pay back; return; surname Huan[cedict]
還
háiㄏㄞˊ
huánㄏㄨㄢˊ
also; in addition; more; still; else; still; yet; (not) yet[cedict]