The correct answer is D.

Explanation: The sentence "I heard he was supposed apology" is incorrect because it uses the wrong form of "supposed" and lacks proper structure. The correct form should involve either "supposed apology" or "he was supposed to apologize," but not in the form shown.

Other options:
- A. I heard his supposed apology: This is correct and means the apology was expected or assumed but might not be genuine.
- B. I heard his unconvincing apology: This is correct and indicates the apology lacked sincerity.
- C. I heard his suppose apology: This is incorrect because "suppose" should be "supposed," but this option is a typo rather than a structural issue.

Thus, "I heard he was supposed apology" is the odd expression.