有几个英语句子没看懂,麻烦解释下1.Itismoredifficulttowritesimply,directly,andeffectivelythantoemployflowerybutvagueexpressionsthayonlyobscureone'smeaning.从than后面开始句式就不懂了,vague和obscure不重复

　　有几个英语句子没看懂,麻烦解释下

　　1.Itismoredifficulttowritesimply,directly,andeffectivelythantoemployflowerybutvagueexpressionsthayonlyobscureone'smeaning.

　　从than后面开始句式就不懂了,vague和obscure不重复吗?

　　2.Thekneeisthejointswherethethighbonemeetsthelargeboneofthelowerleg.

　　joint为什么用复数?

　　3.Acidsarechemicalcompoundsthat,inwatersolution,haveasharptaste,acorrosiveactiononmetals,andtheabilitytoturncertainbluevegetabledyesred.

　　为什么用asharptaste,acorrosiveaction,theability?(冠词不懂）