Here is how you can change them to be correct: 1. Correct 2. I had been given the opportunity to work in Australia .............. OR I had given John an opportunity to work in Australia. 3. I was given an opportunity to work in Australia. 4. I have been given an opportunity to work in Australia.
You remember 'S-V-O', don't you, Vincent-- the most common basic sentence structure? I am speaking of 'O', the object of the verb. Take the sentence,
The armadillo ate the damsel fly.
The subject is armadillo, the verb is ate and the object of the verb is damsel fly. It is the damsel fly which suffered the effects of the verb, so it is the ver