The subject of a sentence in the form of "A dazu B + verb"

Question

What is the subject of this sentence?

Diese Hast und das Laufen, dazu das Stoßen des Wagens, der Benzingeruch und das Blenden von Straße und Himmel hatten sicher schuld daran, daß ich einnickte.

I can think of at least three possibilities

(a) Diese Hast und das Laufen
(b) das Stoßen des Wagens, der Benzingeruch und das Blenden von Straße und Himmel
(c) Diese Hast und das Laufen, dazu das Stoßen des Wagens, der Benzingeruch und das Blenden von Straße und Himmel

If it were an English sentence, I would have liked to see a comma between Himmel and hatten so I can say that (a) was the subject.

As between (a) and (c) as subject, one way to bring out the critical difference may be to ask which of the following is correct:

(x) Diese Hast, dazu das Stoßen des Wagens hatte sicher schuld daran, daß ich einnickte.
(y) Diese Hast, dazu das Stoßen des Wagens hatten sicher schuld daran, daß ich einnickte.

Background: The (first) quote is from Georg Goyert and Hans Georg Brenner's translation of Camus's L'Étranger. For what it's worth (in answering the question), the original goes:

Cette hâte, cette course, c’est à cause de tout cela sans doute, ajouté aux cahots, à l’odeur d’essence, à la réverbération de la route et du ciel, que je me suis assoupi.

Answer 1

• 'Alles' (c) hatte Schuld daran, dass ich einnickte. ;-)

In contrary to english we only use a comma to separate items of an enumeration from each other. There's no need for the last one to be separated from the rest of the sentence unless it is positioned at the end of a clause and needs to be separated from an other clause.

If you used the verb 'sein' than it would be:

• (alle) waren schuld daran...

Or you could even substitute it with a collective expression like 'alles':

• alles war schuld daran...

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But in any case the subject is the whole block!

Answer 2

No addition to mramosch’s answer concerning the question of a), b) or c). Commas in German generally do not denote pauses in speech but rather serve as a separating measure for parts of sentences and the like. As such, there is never, never ever a comma between the subject and the verb of a sentence (assuming SV-word order) unless the subject is a relative clause (which is always separated by commas). Most notably, commas like the one after notably just there are explicitly forbidden in German.

Concerning the question of x) or y), there is sometimes considerable confusion even amoung German speakers. Questions about whether a list requires singular or plural frequently pop up here (and are then often closed as duplicates).

However, there are also rather clear cases like your example. It lists a set of two and explicitly says that both had their share of blame. While technically an argument could be attempted to use singular, the choice of plural just seems so much more natural. Compare:

Hans hat Schuld, dass ich eingeschlafen bin.
Maria hat Schuld, dass ich eingeschlafen bin.
Hans und Maria haben Schuld, dass ich eingeschlafen bin.
Hans, dazu Maria haben Schuld, dass ich eingeschlafen bin.

Die Hast hat Schuld, dass ich eingeschlafen bin.
Das Stoßen hat Schuld, dass ich eingeschlafen bin.
Die Hast und das Stoßen haben Schuld, dass ich eingeschlafen bin.
Die Hast, dazu das Stoßen haben Schuld, dass ich eingeschlafen bin.

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A note on Schuld/schuld: According to the reformed orthography, because one has the blame (in a literal translation) and because you can usually only have objects, i.e. nouns, Schuld in that phrase is nowadays considered a noun and would be capitalised. Ich bin schuld would, however, be considered an adjective and thus written in lower case.