What is the subject of the verb 组成?

Question

北京有各种规模的四合院。最简单的四合院只有一个院子，比较复杂的有两三个，而有钱人家的，通常是由好几座四合院并列组成的。

Hi all. I found this in the Standard Course Book of HSK5, chapter 14.

What is the subject of the verb 组成? The abstract "it", as in English, for example, "it is raining"...?

提前感谢。

Answer 1

The subject is 四合院

而有钱人家的，通常是由好几座四合院并列组成的

If the above sentence confuses you, changing it to the following might help make things clear

而有钱人家的(四合院)，通常是由好几座四合院并列组成的 --> 而有钱人家的四合院，通常是由好几个(院子)并列组成的

A single 四合院 has one courtyard

Some rich people's homes have more than one courtyard. Technically these home should be called 四合院群(Siheyuan Group), however, these 四合院 are one single-family home, and looks like one giant building, so it is easier to just call it 四合院

Answer 2

I think you can identify the subject (noun) by segmentizing the sentence:

通常是由(usually is through)好几座(several)四合院(quadrangle dwellings)并列组成的(made-up in the shoulder-to-shoulder manner)。