The correct option is A Tina suddenly fainted
An idiomatic expression is a type of informal English where the meaning
of the expression is different than the literal meaning of the
expression.
The underlined words "Tina had a blackout" form an idiomatic expression that means 'to be in a semi unconscious state'.
Option A also provides a similar meaning, 'fainted' means 'to lose consciousness'. Hence A is the correct meaning.
Option B: The words 'Tina had a power cut' do not give the correct meaning of the underlined expression. Tina is a person, she does not run on power or electricity. Hence B is incorrect.
Options C and D also do not provide the relevant meaning, considering the context of the sentence ("I got so scared when... I immediately called the ambulance") Hence these options are incorrect.