foreach无法在’方法组’中执行，是否调用方法组，这到底是哪里错了，求大神们帮帮忙

foreach(Book book1 in bll.select)
{
strOut = Replace(strOut, "$BookName$", book1.BookName);
foreach (Book book2 in bll.select)
{
strOut = Replace(strOut, "$BookDetails$", book2.BookDetails);
strOut = Replace(strOut, "$Author$", book2.Author);
strOut = Replace(strOut, "$BookTime$", book2.BookTime);

}
}

foreach 里的 bll.select需要确保能遍历出 关于Book的集合，如果不能直接确保类型，可以打个断点看下。