Explanation:

Let’s break it down one piece at a time:

- Option 1: "since we had"

Here’s the thing: The tense is off. “Since we had missed the bus” sounds odd, because the main verb is “will have to walk” (future). The right way would be “since we have missed the bus” or “since we missed the bus.” “We had missed” suggests the past perfect, which you’d only use if you were already speaking in the past tense.

- Option 2: "We will have to"

That’s fine. It’s talking about something you need to do now—future from the present.

- Option 3: "walk now"

Also good. It just says what’s going to happen.

- Option 4: "No error"

Not correct, because there is an error (see Option 1).

So, ?? Option 1 is the segment with the mistake.

Option 1 is correct.