Create a SQL query to display the names of all employees who work at a specific department.
The SQL query to display the names of all employees who work at a specified department would be:

```
SELECT name FROM employees
WHERE department_id = 21;
```
This query selects the name column from the `employees` table, and then filters the results so that only rows where the `department_id` column is equal to 21 are returned. This would display the names of all employees who work at department 21.
Department ID: 21
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:
Create a SQL query to display the names of all employees who work at a specific department.

### Input:
Department ID: 21

### Response:
The SQL query to display the names of all employees who work at a specified department would be:

```
SELECT name FROM employees
WHERE department_id = 21;
```
This query selects the name column from the `employees` table, and then filters the results so that only rows where the `department_id` column is equal to 21 are returned. This would display the names of all employees who work at department 21.