To determine the correct form of the verb to use in the sentence "The weather … hotter and hotter," we need to consider the context and the grammar rules related to the present continuous tense.

The phrase "hotter and hotter" indicates a continuous process that is happening right now. The present continuous tense is used to describe actions that are currently in progress. The structure for the present continuous tense is:

• Subject + am/is/are + verb-ing

In this case, the subject is "The weather," and the verb is "get." The correct form of "get" in the present continuous tense is "is getting." Therefore, the complete sentence should be:

The weather is getting hotter and hotter.

Let's briefly look at the other options to understand why they are not correct:

• gets: This is the present simple tense, which is used for habitual actions or general truths, not for actions happening right now.
• has been getting: This is the present perfect continuous tense, which is used to describe actions that started in the past and are still continuing. However, it doesn't fit well with the phrase "hotter and hotter," which emphasizes an ongoing process.
• get: This is the base form of the verb and is not correctly conjugated for the sentence.

Therefore, the correct answer is "is getting."