求教单复数问题

请教各位牛人，题目如下：

Judge LF's study asks why some litigants have a preferred status over others in the use of a public resource,the courts, which in theory are available to all but in fact are unequally distributed between...

如果把the courts看作插入语的话，不是应该是is available吗？

从the courts看，a public resource虽然前面有a，但是是一个整体概念，所以用复数。这句子怎么像见过一样的，GMAT里的吗?

多谢啦！这是新东方黄皮书里的一道语法题