【单选题】

In the third paragraph , "three weeks of round-clock effort" means ______.
A．for three weeks the hospital was taking in SARS patients without stopping

B．Dr Urbani worked day and night for three weeks, trying to get SARS under control
C．for three weeks Dr. Urbani did not have any time to sleep, trying hard to fight the new disease
D．After three weeks hard work to control SARS, the hospital superior thought it was time to stop the clock