Order VI Rule 16 of the CPC can be tested in two parts: what kind of pleading it targets, and when the court can act on it.
Test 1, substance:
The rule applies to pleadings that are unnecessary, scandalous, frivolous, vexatious, or likely to prejudice, embarrass or delay a fair trial. The facts given, unnecessary averments that could prejudice or delay trial, fit this description exactly.
Test 2, timing:
The rule lets the court exercise this power at any stage of the proceedings, with no cut-off tied to when the trial starts.
Running the options through both tests:
Rejecting the plaint outright fails Test 1, since that remedy addresses defects in the plaint as a whole under a different provision. Ignoring the pleadings without an order fails because the rule requires an affirmative act of striking out. Restricting amendment to only after trial begins fails Test 2, since the power is not time-locked that way. Only striking out the pleadings, available at any stage, clears both tests.
Order VI Rule 16 exists so a civil suit stays focused on the real dispute and is not weighed down by irrelevant or unfair material in the pleadings. Judging each option by whether it serves that housekeeping purpose shows which one the rule actually supports.
Only striking out the objectionable pleadings, at whatever stage the problem is discovered, actually fulfils the purpose behind Order VI Rule 16.
Therefore, the correct answer is Strike out such pleadings at any stage of proceedings.