Final answer:
In the sentence, 'Fiona is very angry about her boss's decision to sack several members of staff,' the correct preposition to use is 'about,' which shows Fiona's emotional reaction. The correct answer is option 2.
Step-by-step explanation:
The correct preposition to use in the sentence Fiona is very angry ________ her boss's decision to sack several members of staff is 'about'. Therefore, the complete sentence should read: Fiona is very angry about her boss's decision to sack several members of staff. The use of 'about' in this context indicates Fiona's emotional response to the situation which is a reaction to her boss's action.