Fill in the blanks, each using one of the given words or phrases

Fill in the blanks, each using one of the given words or phrases below in its proper form.
bump into   delve into   as for   exposure to  a spectrum of   bear out   within reach of   for the sake of   run out of   take on   be concerned with  comply with
We must_________the reason why he didn't come to the meeting this moming.
【正确答案】：delve into