He was busy writing the exam paper , only ___once in a while to check the time.
The speaker spoke of some writers and some books __________ were popular then.
I refuse to accept the blame for something __________ was someone else's fault.
There is clear evidence __________ the most difficult feeling of all to interpret is bodily pain.
When the news came __________ the war broke out, he decided to serve in the army.
There's a feeling in me __________ we'll never know what a UFO is.