The prices of new houses in our city have been ________than before, but they ______ well at present.

A．higher, still sell

B．lower, are not still sold

C．higher, don’t sell

D．cheaper, are not still sold

（）即根据作者在文章、专著中所开列的参考文献目录，或在文章、专著中所引用的文献名目，追踪查找有关文献资料的方法。

A.计算机文献检索

B.网络搜索引擎

C.参考文献查找法

D.人工文献检索