The correct option is C SQRP
The sentence has four clauses. In first clause, S is the second clause and subordinate, Q is is the third clause subordinate to S, R is the clause subordinate to S and P is the predicate to the main clause. Hence, the structure should be SQRP, that is "The time has come when man must no longer think that the ideal of peace is a distant ideal one which can be postponed for future generations to come." and Option B is correct. The rest of the options do not adhere to this rule, hence incorrect.