The professor explained this theory so clearly that this phenomenon was easy enough ____. [ ]

A. for us to work out

B. working out

C. for working out

D. to working out

评价井以发现工业油气流之后的控制储量所命名的油气田（藏）名称为基础，以井位所在油气田（藏）名称的第二个汉字命名。