______ smoking, he would not have got cancer in the lung.

—Will you read me a story, Mummy? —OK．You    have one if you go to bed right away．

Such a good opportunity may not come again, so you ____________ let it go this time.

 If the island ________ a tourist attraction, last week's earthquake would have caused far more deaths.

If I ______ about this computer program, a hage amount of time and energy would have been saved.