Question

you are about to have dinner不定式和about是什么成分，介词和宾语吗

Answer 1

通常说be about to do sth. 是一个短语，没有进一步研究其成分。细究而言，about是形容词表语（adj. 即将的），不定式是表语补足语。
Ps. 表语补足语的说法不正规，但是可以类比宾语补足语来推论。比如“I want him to go home”中不定式作为宾补，没有的话意思就很奇怪，而类似的about是确定的表语，那么后面的不定式不是补足语的话，还能是什么呢？

Answer 2

这里about是副词 about to do 是带副词的不定式作表语。一般都是把 be about to do看作固定的短语，表示最近的将来，意思是 正要做某事

追问

about是副词，那不定式也可以看成状语咯？总要给不定式一个成分吧

Answer 3

be about to固定用法，将要做某事

Answer 4

谓语:are about to have
宾语:dinner

Answer 5

Peru is a country onthe Pacific coast of South America. It has three main geographical areas: anarrow coastal belt; the Andes Mountains running parallel to the coast; andhigh, flat plains in the southeast. 介词短语on the Pacific coast of South America作定语修饰county中心词。现在分词短语runningparallel to the coast作定语修饰the Andes Mountains中心词，相当于which run parallel to the coast定语从句，其中running: extendin a particular direction(延伸)之意。形容词短语parallel to the coast作方式状语。