On the morning of November 18,1735, an earthquake shook Boston, Massachusetts. John Winthr

op, a professor at Harvard College, felt the quake and awoke. "I rose," Winthrop wrote, "and lighting a candle, looked on my watch, and found it to be 15 minutes after four." John Winthrop walked quickly downstairs to the grandfather's clock. It had stopped three minutes before, at 4 ' 11. Except for stopping the clock, the quake had only thrown a key from the mantel to the floor.

The clock had stopped because Winthrop had put some long glass tubes he was using for an experiment into the box for safekeeping. The quake had knocked the tubes over and blocked the pendulum. Winthrop, therefore, had the exact time that the earthquake had hit Boston. He looked at the key on the floor. The quake had thrown it forward in the direction of the quake's motion by a shock coming from the northwest, perhaps in Canada.

This passage suggests that ______.

A．John Winthrop had difficulty in sleeping

B．earthquakes are common in Boston

C．Boston was a center for clock-making

D．John Winthrop was a scientist