the relative motion of the plates carrying these continents是主语
has been constructed in detail是谓语,后面是并列句
but the motion of the plates with respect to another 是主语
cannot readily be translated into 是谓语
motion with respect to the earth's interior是宾语
这句的of the plates 是介词短语作定语 第一句 是动名词的复合结构 主语 也就是 the relative motion of the plates 是carrying these continents的逻辑主语
第二句 with respect to 是定语 修饰the motion of the plates