According to the author, in which decade of the nineteenth century did a steamship first attempt to compete with the transatlantic packets

A．Getting off to work with a minimum effort helps save one's energy.
B．Dr. Kleitman explains why people reach their peaks at different hours of day.
C．Habit helps a person adapt to his own energy cycle.
D．Children have energy cycles, too.

A．change his energy cycle
B．overcome his laziness
C．get up earlier than usual
D．go to bed earlier