Explanation:

- Let's review the options to substitute the underlined word:

1. It’s: This is the contraction for "It is" or "It has." In the sentence, "It's time we left to the airport," "It’s" correctly fits, meaning "It is time..."

- Correct Answer

2. It was: "It was time we left to the airport" suggests the action should have happened earlier. Not the best fit for a present suggestion.

3. It has: "It has time we left..." is grammatically incorrect in this context.

4. It: "It time we left..." is incomplete and incorrect.

- Therefore, Option 1 ("It’s") is the right substitution.