A、BECAusE it is rEAlly tough For pArEnts to EnForCE BEDtimE.
B、BECAusE it is BiologiCAlly DiFFiCult For stuDEnts to risE EArly.
C．BECAusE stuDEnts work so lAtE At night thAt thEy CAn’t gEt up EArly.
D．BECAusE stuDEnts ArE so lAzy thAt thEy Don’t likE to go to sChool EArly.