Complete the following sentence :
Elephants produce ............. sound.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks to complete the sentence "Elephants produce ............. sound." We need to determine what type of sound elephants produce.

2. **Researching Elephant Communication**: Elephants are known for their unique communication methods. They can produce sounds that are not audible to humans.

3. **Identifying Sound Frequencies**: The human hearing range is typically between 20 Hertz (Hz) and 20,000 Hz. Sounds below 20 Hz are not heard by humans.

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