"had'nt" versus "have'nt"

[Petro]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #115 "Tense Agreement", question 7

I must admit I ......... thought how the story would finish before I read the book.

(a) haven't
(b) hadn't
(c) aren't
(d) couldn't

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #115 "Tense Agreement", answer 7

I must admit I hadn't thought how the story would finish before I read the book.

Correct answer: (b) hadn't

Your answer was: incorrect
I must admit I haven't thought how the story would finish before I read the book.
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when can had'nt or have'nt use in sentences

Petro

[Mister Micawber]

.
Haven't (present perfect) refers to a period from the past until the present time; hadn't (past perfect) refers to the earlier of two past events.

In this case, though, I am wondering which was intended-- Read is both the present and past form of the verb.
.
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Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mr. Micawber