困难同义词

difficult season───困难季节

difficult opponent───难对付的对手

difficult birth───难产

difficult issue───难题

difficult match───困难的比赛

difficult period───困难时期

difficult position───困境

difficult process───艰难的过程

difficult question───难题

For the reasons of preserve situation and the difficulty of preparation, there are a lot of synonym and the nomen dubium in the published taxa.───由于化石的保存状况以及标本的修理难度等多种原因，已经发表的材料中包括了大量的同物异名现象以及无效的属种。