Select the most appropriate option to fill in the blank and make a grammatically correct sentence.

Children are not allowed to use the swimming pool ______they are accompanied by an adult.

unless

The most appropriate option to fill in the blank and make a grammatically correct sentence is:

☀ unless

The sentence would read: "Children are not allowed to use the swimming pool unless they are accompanied by an adult."

Explanation: "Unless" is used to indicate a condition that must be met for something else to happen. In this context, it conveys that the condition for children to use the swimming pool is being accompanied by an adult. The other options don't fit the context:

• At least: This phrase is used to indicate a minimum or a lower limit, but it doesn't convey the same idea as the sentence.

• If only: This phrase is used to express a wish or desire, and it doesn't fit the context of a condition for using the pool.

• In case: This phrase is used to indicate preparation or precaution for a possible event, but it doesn't fit the context of a condition for using the pool.