Step 1: Understand the situation.
Under the Code of Civil Procedure, 1908, a suit has abated because the legal representatives of a deceased party were not brought on record in time. The plaintiff now wants the abatement set aside. We must find what he has to show.
Step 2: What does abatement mean?
When a party dies and their legal representatives are not added within the prescribed time, the suit abates, meaning it dies. Order XXII of the CPC handles this.
Step 3: Can a fresh suit be filed?
Order XXII Rule 9 says that once a suit abates, no fresh suit can be filed on the same cause of action. So the only way forward is to revive the abated suit.
Step 4: How can the abatement be set aside?
The plaintiff may apply to the court to set aside the abatement. The court has discretion to allow this if the applicant shows sufficient cause for not bringing the legal representatives on record within time.
Step 5: Match with the options.
Option D says sufficient cause for not making the application within time. That is exactly the test under Order XXII. So D fits.
Step 6: Eliminate the wrong options.
Option A (decree not yet passed) is irrelevant to setting aside abatement. Option B (error apparent on the face of record) is the test for review, not abatement. Option C (defendant had knowledge of death) is not the required showing. So A, B, and C are wrong.
Step 7: Final answer.
\[ \boxed{\text{Sufficient cause for not making the application within time.}} \]