--Why are you so anxious? --It isn’t your problem ____.
It suddenly occurred to him ________ he had left his keys in the office.(2012·江西)
Have you noticed the problem ________ he is now in low spirits?________ come?
When the news came ________ the war broke out,he decided,to serve in the army.
________ was known to us all that Johnson had broken his promise ________ he would give each of us a small gift.
Modern science has given clear evidence ________ smoking can lead to many diseases.(2011·天津,13)