He is busy right now, but if he ____, he would help us.
(A) was (B) were (C) wasn't (D) weren't
I think the answer is option D. Am I right?
Although pedants will disagree, many native speakers of BrE would be happy with 'wasn't'
I wouldn't use it and can't say that I like it, but it's so common that it doesn't sound wrong.
1. We often use were instead of was after if. This is common in both formal and informal styles. In a formal style, were is more common than was, and many people consider it more correct, especially in American English. Swan, Michael (2005.235) Practical English Usage, 3rd edn, Oxford: OUP.
2. (i) If it was/were to rain, the ropes would snap. […]
As (i) illustrates, both the past subjunctive and the past indicative forms are possible for hypothetical conditions, the subjunctive being preferred by many, especially in formal written English:
If John was/were here, we would soon learn the truth.
The idiom if I … you by convention usually contains the subjunctive were, though was also occurs frequently. Quirk, Randolph, Greenbaum, Sidney, Leech, Geoffrey and Svartik, Jan (1985.1093-4) A Comprehensive Grammar of the English Language, London: Longman
3. In popular and non-formal speech and writing, the were-subjunctive is often replaced by the indicative was, which brings this verb into line with other verbs, where the past tense is similarly used for hypothesis about the present and future […]. Were is, however, widely preferred in If I were you. Sylvia Chalker in McArthur, Tom (1992.997-8) The Oxford Companion to the English Language, Oxford: OUP
4. In most informal contexts, indicative forms of be are preferred, except for the semi-fixed expression if I were you. Carter, Ronald & McCarthy, Michael (2006.756) Cambridge Grammar of English, Cambridge: CUP
5. Although sentences of the type [If I were you, I’d leave him] continue to be used, there is increasing use of was instead of were in these types of sentences in contemporary spoken English. Yule, George (1998.131) Explaining English Grammar, Oxford: OUP
6. The Past Subjunctive […] survives as a form distinct from the ordinary Indicative Past Tense only in the use of were, the Past Tense form of the verb to be with a singular subject […]. Like the Present Subjunctive, this is nowadays fairly infrequent, and is often replaced by Past Indicative was. Leech, Geoffrey, (2004.115) Meaning and the English Verb. 3rd edn, Harlow, Pearson Longman
7. […] especially in informal English. When we are talking about an unlikely situation, you use the simple past tense in the conditional clause, and ‘would’, ‘should’ or ‘might’ in the main clause. […]
I should be surprised if it was less than five pounds. […]
In the conditional clause, ‘were’ is sometimes used instead of ‘was’, especially after ‘I’.
If I were as big as you, I would kill you. Sinclair, John (Editor-in-Chief), (1990.351) Collins Cobuild English Grammar, London: HarperCollins
8. The so-called past subjunctive (also called the were-subjunctive) is used in clauses of hypothetical condition. It differs from the past indicative of be only in the first and third person singular, which popularly replace it. […]
If I were you, I’d own up. (If I was you …). Chalker, Sylvia and Weiner, Edmund (1993.381-2) The Oxford Dictionary of English Grammar, 2nd edn, Oxford:OUP
9. Was has been in competition with were for 300-400 years, and in general the usage manuals regard it as acceptable, though less formal than were. […] if I were you bears some resemblance to a fixed phrase, and was is less usual here than in conditionals generally.Huddleston, Rodney & Pullum, Geoffrey K (2002.86) The Cambridge Grammar of the English Language, Cambridge: CUP
10. Were as the past singular subjunctive form has held out a little more tenaciously, partly because in the stereotyped phrase “If I were you” the complement you has by attraction tended to establish it […] In the following sentence, for example, our modern tendency would be to turn the subjunctive were into a blunt indicative:
It is high time the wide field of Tudor music, both secular and sacred, were explored by many more schools. Vallins, G H, (1951.68) Good English, London: Pan
Also, quite a lot of people who say If I were you are happy to say I wish I was.