2. You __ pay for parking when you see a parking meter. are allowed must not must

## Step 1<br />The problem is a fill-in-the-blank type question, which tests the understanding of modal verbs in English. Modal verbs are auxiliary verbs that express necessity, possibility, permission, or ability.<br />## Step 2<br />In this context, the sentence is about the obligation to pay for parking when you see a parking meter. The modal verb that best fits this context is "must", which expresses a strong obligation or necessity.<br />## Step 3<br />Therefore, the correct answer is "must".