Select the sentence that uses the idiom correctly.

She missed the exam as she felt under the weather.

The idiom "under the weather" means to be feeling unwell or sick. It is not used to describe the weather.

So, the sentence that uses the idiom correctly is She missed the exam as she felt under the weather.

The other sentences are incorrect because they use the idiom to describe the weather.

• Flowers bloom when the weather is nice.
• Trees shed their leaves when the weather gets cold.
• Reena was walking on the lawn when the weather was nice.