How can the operator sign the test record using the touchscreen?

The correct answer indicates that the operator can sign the test record using either a stylus or their finger on the touchscreen. This flexibility in input methods is designed to enhance usability and allows operators to choose the method that they find most comfortable or convenient. Touchscreens are integrated into the Intoxilyzer 9000 system to streamline the testing process, and supporting both a stylus and finger ensures that operators can sign with precision or ease, depending on the circumstances.

The other options provided do not account for the full range of input methods. For example, saying only a finger can be used limits the operator's choice and does not align with the intended functionality of the touchscreen interface. Additionally, using an external mouse is not a standard practice for signing test records in a system that emphasizes touchscreen capabilities. Finally, while voice commands are increasingly common in technology, they are not typically employed for this specific function on the Intoxilyzer 9000. Hence, the option that incorporates both a stylus and a finger represents the actual operational capabilities of the device.