一. 连词：but, however, although, while

1.连接两个并列分句 Honey is sweet, but the bee stings. I ought to have helped her, but I ever could.

2. 连接两个并列成分 They see the trees but not the forest.

He no longer felt disappointed, but happy and hopeful.

二. 后接状语 He tried to save it, but in vain. He glanced about, but seeing only the empty room.