Protactinium has a half-life of 70 s. A sample of protactinium is prepared and monitored over a period of time. Which of the following statements is correct?
A The activity of the protactinium will be zero after 140 s.
B The activity of the protactinium will be 25% of its initial value after 140 s.
C The activity of the protactinium will be 12.5% of its initial value after 280 s.
D The activity of the protactinium will never become zero.