Formal language I believe that is the right language
Http://digital.library.upenn.edu/women/keller/life/life.html
Answer:
Ocean currents can be caused by wind, density differences in water masses caused by temperature and salinity variations, gravity, and events such as earthquakes or storms.
For the main reason that "it promoted sacrifice for the common good." the speech was commonly read during the Cultural Revolution. This speech was the primary political propaganda of Mao Zedong as a slogan during the dark times of the Chinese cultural history.
The answer is B. Therefore
