When_____the accident________?

He was so deep in thought，thinking of the problem ________ he knocked into the tree without noticing it

leaving office in 1999, Nelson Mandela didn’t stop doing he thought was right.

On hearing the news that her husband was killed by Pakistan separatists，the wife ______.[ ]

A man needing a heart transplant was told the only heart available is ________ of a sheep.When asked how he was feeling after the operation, he replied “Not B-A-A-A-A-D!”