一、AAA型（原形、过去式和过去分词同形）：
cost cost cost 
cut cut cut 
let let let 
put put put 
read read read 

二、ABB型（过去式与过去分词同形）：
bring brought brought
build built built 
buy bought bought
catch caught caught 
dig dug dug
feel felt felt 
find found found
get got got 
have had had
hear heard heard 
hold held held
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          七分之二的分子、分母都加上（     ）以后，约分结果是三分之二。                 

           有100个连续的自然数的和是8450，这100个连续自然数中的第一个自然数是（　    ）。

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