Until I heard him myself, I … imagined that he said that

Analyze the question: The sentence is "Until I heard him myself, I __ imagined that he said that." We need the modal phrase that fits the past time frame ("Until I heard...") and the meaning of disbelief.

Concept: "Could not have + past participle" expresses the impossibility or disbelief of something in the past. Here, the speaker is saying that before hearing it personally, it was unthinkable that he would say such a thing. Also, the verb "imagined" is a past participle form following the auxiliary, so we need an auxiliary phrase ending in "have."

Check each option:

• A. "did not imagined": Wrong. After "did not," the verb must be in base form (imagine), not "imagined." Ungrammatical.
• B. "could not have imagined": Correct. "I could not have imagined that he said that" is grammatical and fits the past context and meaning of disbelief.
• C. "should not have imagined": Grammatical, but it means "it was wrong of me to imagine," which doesn't fit the meaning of "until I heard him myself."
• D. "will not have imagined": Wrong. "Will" is a future/prediction form and clashes with the past tense "heard."

Answer: Option B.

Tip: In "fill-in-the-gap" questions, first check grammar (what verb form must follow?), then check tense consistency, and finally meaning. "Could not have + past participle" is a favorite pattern in WASSCE and JAMB for expressing past impossibility.