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
_________________________

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.
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber