题目内容
－Sixteen-year-olds ________ to drive．
－I agree．They aren't serious enough at that age．
shouldn't be allowed
shouldn't allow
don't allow
are allowed not
天天练口算系列答案小博士：仔细观察下面的基数词和对应的序数词的区别和变化，你会发现这种变化是有规律的，你能归纳出来吗？请根据规律填出所缺的基数词和序数词，并特别注意黑体字的词。
one | first | eleven | eleventh | twenty-one | twenty-first |
two | second | twelve | twelfth | twenty-two | twenty-second |
three | third | thirteen | thirteenth | twenty-three | twenty-third |
four | fourth | fourteen | fourteenth | twenty-four | ______ |
five | fifth | fifteen | ______ | twenty-five | twenty-fifth |
six | sixth | sixteen | sixteenth | twenty-six | twenty-sixth |
seven | ______ | seventeen | seventeenth | twenty-seven | twenty-seventh |
eight | eighth | eighteen | eighteenth | twenty-eight | twenty-eighth |
nine | ninth | nineteen | nineteenth | twenty-nine | twenty-ninth |
ten | tenth | twenty | twentieth | thirty | thirtieth |
thirty-one | thirty-first fortieth ninetieth | hundred | hundredth | ||
forty | thousand | thousandth | |||
ninety | million | millionth | |||
我找到规律了！请看：
1 英语序数词1～19，除first，second，third等特殊形式外，其余的一般是在相应的基数词后加-th构成。
2 有几个序数词加-th时拼法不规则，要注意。如fifth，________ ________ ________。
3 十位整数的序数词的构成方法是先将其基数词的词尾“ty”中的“y”改为“i”，再加“-eth”。如________。
4 基数词“几十几”变成序数词时，只需将个位数变成序数词，十位数不变。如________。