Why it is used "was going to"?

[Dima]

English Language Tests, Intermediate level

ESL/EFL Test #154 "English grammar and vocabulary questions", question 5

I thought Nancy said she ......... spend the weekend with her parents.

(a) should
(b) will
(c) is
(d) was going to

English Language Tests, Intermediate level

ESL/EFL Test #154 "English grammar and vocabulary questions", answer 5

I thought Nancy said she was going to spend the weekend with her parents.

Correct answer: (d) was going to
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why it is used was going to? Going to is used only that is very sure.The person said that I thought so it is uncertain. So why it is used going to.

Dima

[Mister Micawber]

.
'I' (the speaker) 'thought', but Nancy was very sure.
.
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Native English teacher at Mister Micawber's

[Saneta]

why not: should?

thanks

[Beeesneees]

There is a context where that would be correct (though it isn't as common).
Perhaps the test creator will consider changing that question.
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Cheers m' dears!