Exercício: AFA - 2014 - if clauses

Hello guys! On sunday morning,had started the test of afa(air force academy) so, at english test i saw this question, and it make me had doubts.

32) Mark the right option to complete the statement.

"If the plane hadn't been delayed in taking off, the passengers ________ about the events in New York and Washington.

a) woudn't have known (the right answer)
b) shouldn't have known (my answer)
c) would know
d) hadn't known
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Letter A is correct.

Should (past form of shall) "...Shouldn't have known" It sounds strange

If you are Brazilian: O should é o nosso ("deveria") e o would have ("teria") o would do ("faria") o would go ("iria") e assim por diante.

Best Regards
Thank you Daniel! A tradução para o portugues ficaria assim? : "Se o avião não tivesse atrasado sua decolagem, os passageiros não teriam conhecimento sobre os acontecimentos em Nova Iorque e Washington." Grato.
Hello,

exactly man!

I hope I've helped you!

See you!