根据要求写出下列单词。 1.upstairs (反义词) ___________________ 2.by air (同义词) _____________________ 3.never (反义词) _____________________ 4.sheep (复数形式) ___________________ 5.reporter (动词) _____________________ 6.busy (副词) _______________________ 7.second (基数词) ___________________ 8.noisy (名词) _______________________ 9.children (单数) _____________________ 10.die (形容词) ______________________