询根问底

lit. to examine roots and inquire at the base (idiom); to get to the bottom of sth

to ask about / to inquire about

root / basis / classifier for long slender objects, e.g. cigarettes, guitar strings / CL:條|条[tiao2] / radical (chemistry)

to ask / to inquire

to ask; to inquire

(equivalent to 的 as possessive particle)

background / bottom / base / end (of the month, year etc) / remnants / (math.) radix / base