用a还是an,取决于后面单词的第一个音标,如为元音用an,为辅音用a。useful的第一个音是辅音所以应把an改为a。类似的,我们说a European country. 2. Plane is a machine that can fly. Plane为可数名词单数,不能单独放在句中,应在其前加冠词或把它变为复数,而本句后有a m...
, a Chinese great navigator Zheng He embarked on the voyages to the West Oceans for seven times, bringing tea leaves, silk and porcelain as trading goods, instead of war, s...
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