The shopkeeper said they had sold out the shoes ____ your si

当然是B了,英语不能用语文来解释的哦亲,in one's size 是固定语法搭配的,记住就行啦,下面是about 的具体用法,亲,要仔细看哦.
副词 adv.大约；差不多
a little more or less than; nearly
· We waited for about twenty minutes.
我们等了差不多二十分钟.
副词 adv.几乎一样；近于
almost exactly
· Peter is about as tall as John.
彼得几乎和约翰一般高.
副词 adv.在附近某处；不远
somewhere near; not far away
· Is the manager about?
经理在（附近）吗?
副词 adv.到处；各处
here and there; in different ways or places
· The children were running about in the rain.
孩子们在雨中跑来跑去.
· He is always leaving his papers about.
他总是把文件到处乱放.
介词 prep.附近；周围；各处
around; here and there
· There were a lot of flowers about the house.
房子周围有许多花.
· Their house is about here on the map.
从地图上看他们房子在这附近.
· He planted trees about the house.
他种树于屋子四周.
· I dropped the key somewhere about here.
我把钥匙失落在这个地方附近.
· We walked about the town.
我们在城里到处走动.
介词 prep.关于；有关
of,on the subject of
· The story is about giants.
这是关于巨人们的故事.
· They're full of good advice about reading.
那里边尽是关于阅读的金玉良言.
· I read about it in the newspaper.
关于那件事我是在报纸上看到的.
· Are you talking about me?
你们在谈论我么?
· I want to ask about the train time table.
我要查询一下火车行车时间表.
· What's he so angry about?
他恼怒什么?
· Her mother was anxious about her.
他母亲挂念她.
介词 prep.（时间）近于
a little before or after a time
· Come about six p.m..
下午六点左右来.
· He left there about ten o'clock.
他大约在十点钟离开了那里.

答案选B（in ）
in one's size...为固定搭配。
例如：You can wear your mom's shirt,it's in your size.[你可以穿你妈妈的衣服，是你的尺寸。]

不关语法的问题也不是翻译的问题 他们通常是这样搭配的...同学你初三或要升初三了吧 我以前也做过这道题 我们老师就说是一般是这样搭配的