Fill in the blanks with the most appropriate option:-

If I ……… you, I would have grabbed the opportunity.

were

The correct option to fill in the blank is were.

The sentence is in the subjunctive mood, which is used to talk about hypothetical situations. In this case, the speaker is imagining what they would do if they were in the other person's shoes. The verb "were" is used in the subjunctive mood to talk about hypothetical situations in the past.

The other options are not as appropriate:

• Was is the past tense of "be". It would not be accurate to use the past tense, as the speaker is not talking about something that happened in the past.
• Shall be is the future tense of "be". It would not be accurate to use the future tense, as the speaker is not talking about something that will happen in the future.
• Am is the present tense of "be". It would not be accurate to use the present tense, as the speaker is not talking about something that is happening right now.