The correct option is B Australia was defeated by India in the 20-20 world cup cricket finals.
Active voice is when the subject does an action. Passive voice is when the subject receives an action.
When you change a sentence from active to passive, you change the position of the subject from subject to object. The same goes for the object.
In order to keep the meaning unchanged, words like 'by' are introduced to say that the action is performed 'by' the object (original subject.)
While changing from active voice to passive, the form of the verb changes. But, the tense does not change.
Option A: In the given sentence, the verb form 'defeated' changes to 'was defeated', the new subject is Australia.
Hence, the sentence will be: Australia was defeated by India in the 20-20 World Cup cricket finals. So, option A is correct.
Option B is incorrect because 'was' and 'by' are not added. This changes the meaning of the sentence.
Option C is incorrect because the tense has changed. It indicates the past perfect continuous tense.
The tense of the given sentence is in simple past, and must remain in the same tense.
Option D is incorrect for the same reason. The tense has changed to past continuous tense.