An effective way to make language more emphatic when using English is by inverting a sentence's normal word order.
For example, 'I have never eaten such a flaky croissant.' is a regular sentence, with the word order: subject (I) + verb (have never eaten) + object (such a flaky croissant).
To add emphasis, the auxiliary verb comes before the subject: Never have I eaten such a flaky croissant. ('Never' is an adverb and the main verb is 'eaten')
In option A, the sentence has the word order: auxiliary verb (Had) + subject (I) + main verb (known) + object + clause. The sentence has altered the normal word order, hence option A is correct.
Option B is incorrect because the sentence has the normal word order, beginning with the subordinating conjunction "If", followed by the subject and the rest of the sentence.
Options C and D also have the normal word order, with the addition of the phrase "I wish" and the adverb "Only", hence they are incorrect.