it can be shared by anyone__is close，是who还是whom？

Question

这是完型填空里的一句话，横线处应该是who还是whom？by后面应该是宾格，所以应该是whom，但为什么答案是who？
完型全文如下：
People all over the world celebrate Valentine’s DayHowever,the holiday 26 differently in different countries 27 each culture has its own Valentine’s Day customs For examplepeople in the United States and Japan both celebrate Valentine’s Day 28February 14But in Japanonly romantic partners come together,while in Americait can be shared by anyone 29 is closefriend or loverChocolate is the most preferred gift in the US 30 it is common in JapantooHowever,in the US other kinds of gifts are 3 1 givenand many people exchange cards The biggest 32 is that in Japanonly girls and women33 chocolates to boys and menbut in the US boys and girls will give cards or small gifts to all of 34 friendsAnd while American men and women both receive giftswomen usually get 35 expensive gifts than menThat’s why I would like to be a man in Japan but a woman in the US!

Answer 1

【考查】同位语
【难度】中
【题源】2012年广州英语中考试卷
【解析】一个名词(或其它形式)对另一个名词或代词进行修饰，限定或说明，这个名词（或其它形式）就是同位语。本题空格中作为anyone同位语，所以应该用who（同位语从句中who作主语，whom是宾语形式，不符题意）
【例句】Yesterday I met Tom,a friend of my brothers'. 昨天我遇到了我弟弟的朋友汤姆。
（a friend of my brothers'是受词Tom的同位语，指同一人）
【答案】who

Answer 2

因为它后面的句子中是作为主语用的，所以得用who，不是用whom.前面的by已经有宾语anyone了。

明白了吗？

Answer 3

在从句 who is close frend or lover 里做主语。