Read the passage and answer the below question:At last the bomb was made. The site chosen for the test explosion was the desert region two hundred miles from Los Alamos. Ten seconds before Zero hour, a green flare warned the spectators to keep down. Then came the blinding flash. The whole area was suddenly brighter than the brightest daylight, and the bomb was a ball of fire. Then came thetremendous roar and the heavy pressure wave, which knocked down two men outside the control center. And then came the cloud - the mushroom cloud, all the colours of the rainbow, ironically beautify, surging up to over 40,000 feet-over 10,000 feet higher than Everest.Which of the following best helps to bring out the precise meaning ofZero hour??

• A. twelve O'clock at night
• B. twelve O' clock in the middle of the day
• C. exact time at which operations are to begin
• D. time for spectators to keep quiet