I’m quite familiar ___ the writer who wrote these songs

Who do you think can do the voluntary work—______ who is willing to help can do it.

The charity organization has launched a TV appeal _______ people should do as much as they could to help those survivors in the earthquake.

The engineers are going on with their highway project, _____the expenses have risen

David, you clean the blackboard today, ____?— With pleasure. I cleaned it yesterday, though.[ ]