A．post-graduate studentsB．senior university studentsC．p……

单项选择题A．underwater explosionsB．oil and gas explorationC．whistling of shipsD．sonar navigation

单项选择题______ is the main object of study of phonology.

单项选择题In ______, President Nixon met Mao Zedong and the two countries issued the Shanghai Communiqu.

单项选择题The Vietnam War started in ______ and ended in______.

单项选择题______ was the author of The Great Gatsby.