Not until _____,_______the diffiult problem.[ ]

A.did he return;we settled

B.he returned;we settled

C.did he return,did we settle

D.he returned;did we settle.

“杵臼之交”多用来指不计身份而结交的朋友。这里的“杵臼”在古代是用来做什么的( )

A．打水

B．磨面

C．捣米

D．榨油