1. The boss wants to hire an useful person. 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...
which looks like a snail without a shell, lays down a slimy trail over which it crawls. It uses so much energy producing the slimy mucus and crawling over it that a mouse traveling the same distance uses only one twelfth as much energy...
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