A great deal of research(do)______the possible causes of cancer.(现在完成时) He wanted nothing except(leave)______peace. The man who(bite)______a snake was treated with serum.
A great deal of research(do)_being have done_____the possible causes of cancer.(现在完成时) He wanted nothing except(leave)_being__leaven with___peace. The man who(bite)__biten by____a snake was treated with serum.