Yuan Longping did all he could ________ himself ________ the scientific research on rice．
A.to apply; toB.to apply; forC.to apply; atD.to devote; for在线课程A
apply oneself to…意为“专心于……；致力于……”。apply for意为“申请”。devote oneself to…意为“奉献于……；致力于……”。