下面的句子里的had是过去完成时的用法吗?过去时和过去完成时,现在完成时的区别是什么?不要大段的理论描述.例子：it doesn't help that building a big ,powerful dam had become a s

下面的句子里的had是过去完成时的用法吗?过去时和过去完成时,现在完成时的区别是什么?不要大段的理论描述.例子：it doesn't help that building a big ,powerful dam had become a symbol of achievement for nations and people striving to assert themselves.