Transform the below sentence by replacing the word-"if" with the most appropriate word:
If the vehicle had been parked in the wrong place, it would have been towed away.
In the given sentence, the clause, 'If the vehicle had been parked in the wrong place' is in the past perfect tense. The auxiliary verb, 'had' is used along with the past participle form of the main verb (parked). In such clauses, the word, 'if' can be omitted and the sentence can be transformed by inverting the subject and the auxiliary verb, 'had'. In the given sentence, the subject is 'the vehicle'.
Option B: 'Whether' is a conjunction which is used to express a choice between two alternatives or events. Here, there is no such reference. Hence, this option is incorrect.
Option C: The modal, 'should' is used along with the simple present form of the main verb. Example: 'Should I have lots of money' is the correct usage. Hence, this option is incorrect.
Option C: The word, 'unless' is used to replace 'If... not'. In the given sentence, the word, 'not' isn't used. Hence, this option is incorrect.
Option D is incorrect as a conditional sentence does not start with the word, has'. This is grammatically incorrect.