B
分析:首先,要看分?jǐn)?shù)是否是最簡(jiǎn)分?jǐn)?shù),不是的,先把分?jǐn)?shù)化成最簡(jiǎn)分?jǐn)?shù),再根據(jù)一個(gè)最簡(jiǎn)分?jǐn)?shù),如果分母中除了2與5以外,不再含有其它的質(zhì)因數(shù),這個(gè)分?jǐn)?shù)就能化成有限小數(shù);如果分母中含有2與5以外的質(zhì)因數(shù),這個(gè)分?jǐn)?shù)就不能化成有限小數(shù);據(jù)此逐項(xiàng)進(jìn)行分析后再選擇.
解答:A、

是最簡(jiǎn)分?jǐn)?shù),分母中只含有質(zhì)因數(shù)7,所以

不能化成有限小數(shù);
B、

化簡(jiǎn)后是

,分母中只含有質(zhì)因數(shù)2,所以

能化成有限小數(shù);
C、

化簡(jiǎn)后是

,分母中只含有質(zhì)因數(shù)7,所以

不能化成有限小數(shù);
故選:B.
點(diǎn)評(píng):此題主要考查什么樣的分?jǐn)?shù)可以化成有限小數(shù):必須是最簡(jiǎn)分?jǐn)?shù),分母中只含有質(zhì)因數(shù)2或5.