CFA Mock Morning session Quants Q25 please, reading, solution, question, either

Makavelim3

I have been scratching my head for this question but it doesn't make any sense to me even after reading the explanation. Although I don't know what should be the solution for this question but I am not convinced the explanation either. Can any one of you please explain how P(A or B) and P(A or B or AB) are the same probabilities?