Do you have__books?Yes,I do .A.many B.some 我知道选B,但A为什么不行呢?

接触多了以后就不会问了。

英语有时候没那么多为什么，语言规定是这样就是这样~

牛津高阶英汉双解词典
some 1
/ səm; səm/ indef det (used in affirmative sentences,or in questions expecting a positive reply; after if/whether, when the sentence has a positive emphasis; and in invitations and requests 用於肯定句或希望得到肯定回答的问句; 置於if/whether之后, 语义偏重於肯定; 用以表示邀请和请求)
(used with [U] ns 与不可数名词连用) an unspecified amount of 一些; 若干: There's some ice in the fridge. 冰箱里有些冰块儿. * Some mail came for you this morning. 今天上午有你的邮件. * You left some money on the table. 你把钱落在桌子上了. * Would you like some milk in your tea? 要不要在茶里加点儿牛奶? * Isn't there some (more) wine in the cellar? 酒窖里（还）有酒吗? * If you save some money each week, we can go on holiday. 要是你每星期能存点儿钱, 咱们就可以外出度假了. * Please have some cake. 请吃点儿蛋糕.
(used with pl [C] ns, usu referring to three or more 与复数可数名词连用, 通常指三个或三个以上) an unspecified number of 一些; 若干: Some children were playing in the park. 有些小孩儿在公园里玩儿. * Why don't you give her some flowers? 何不送给她一些花? (Cf 参看 I suggest you give her some flowers.) * Didn't you borrow some records of mine? 你没向我借过一些唱片吗? (Cf 参看 You borrowed some records of mine, didn't you?) * If you put some pictures on the wall the room will look brighter. 你要是在墙上挂几幅画, 这个房间就更有生气. Cf 参看 any1. some 2
/ sʌm; sʌm/ indef det
(used with [C] and [U] ns 与可数和不可数名词连用) (a) a number or amount of sth that is less than the total being considered 部分; 有些: Some people have naturally beautiful voices while others need to be trained. 有些人生就一副好嗓子, 有些人则需要训练. * Some modern music sounds harsh and tuneless. 现代音乐中有一些又刺耳又不成调子. (b) a considerable number or amount of 相当多的; 好些: We went some (ie several) miles out of our way. 我们偏离原定路线走了好几英里. * That is some help to us, ie It helps to a certain extent. 那对我们很有用. * I shall be gone (for) some time, ie for quite a long time. 我将有好些日子不在这儿. * The headmistress spoke at some (ie considerable) length. （女）校长讲话讲了好一会儿.
(used with sing [C] ns 与单数可数名词连用) person, place or thing that is unknown or unspecified 未知的或未确指的人、 地点或事物: Some man at the door is asking to see you. 门口有人要见你. * She won a competition in some newspaper or other. 她参加某报纸举办的比赛获胜.
(used with numbers 与数词连用) approximately 大约; 近於: He spent some twelve years of his life in Africa. 他在非洲度过了近十二个年头. * Some thirty people attended the funeral. 参加葬礼的约有三十人.

语感问题 外国人不这么说 语法角度是对的

1 从语法上：some 和many都是对的
2 我们单单把这句话拿出来说：没有前后文,也没有任何情景 ：do you have some books?你有些书吗?do you have“ many”(有点强调的意思) books 你有许多的书吗?也都是对的.
3 但是作者想问的就是平常话：Do you have some books?“嘿,你有书吗?（借我来几本看看）并不是”你有许多书吗“（这句一般是在特定的情景中说的）
4 英语学习不要死扣语法、直译,更多的是意译、体会,增加自己的语感,达到和别人对话的能力,这才是学习英语的目的（当然现在是应试教育多）