We asked him why he ________ telephoned earlier.

Explanation of all the options:

1.did not

• Explanation: "Did not telephoned" is grammatically incorrect because it combines the past simple with the wrong form of the verb (should be "did not telephone"). However, it also doesn't fit well in this context of a reported question about a past event.
• Incorrect ❌

2.has not

• Explanation: "Has not telephoned" uses the present perfect tense, which does not align with the past context implied by the word "asked." The sentence is referring to a past inquiry about a past action.
• Incorrect ❌

3.had not

• Explanation: "Had not telephoned" is the correct form here. It uses the past perfect tense, which is appropriate because it indicates an action that did not happen before another past action (the asking).
• Correct ✅

4.would not

• Explanation: "Would not telephoned" is incorrect because it combines "would" (which implies a conditional) with the past tense form of the verb (again, should be "would not telephone"). It does not fit the context of asking about a past action.
• Incorrect ❌

5.was not

• Explanation: "Was not telephoned" is also incorrect because it uses the past tense but incorrectly implies that the telephoning action is being described as an ongoing situation rather than focusing on the action itself.
• Incorrect ❌