A．They noticed an apparent change in the position of the North Star.
B．They observed eclipses at different times of the year.
C．They were the first to estimate the distance between heavenly bodies.
D．They wanted to prove that the Earth was fiat.

A．One of the students asked him about it in the previous class.
B．He read about it the previous day.
C．He had just read Dr. Frederick Cock's travel log
D．The students were required to read about it for that day's class

A．Pierre had announced his success prematurely.
B．The investigation of Pierre's expedition wasn't thorough.
C．Pierre wasn't an experienced explorer.
D．He had reached the pole before Pierre did.