When preparing for a webinar, it is crucial to ensure that all necessary multimedia hardware is functional for both input and output devices. The three key hardware components to test and configure in a webinar setting are:

C. Speakers: The user must test and configure speakers to hear the audio during the webinar, such as the presenter's voice or any media shared.

E. Camera: The camera is essential for video communication, allowing the user to broadcast their image to others in the webinar. Many webinar platforms will have settings to test and adjust the video feed from the camera.

G. Microphone: A functional microphone is critical for the user to participate verbally in the webinar. The user should test this to ensure that they can be heard clearly by other participants.

Why the other options are incorrect:

A. Keyboard: While it might be used to type messages or navigate, it’s not necessary to test the keyboard specifically for webinar participation.

B. Digital pen: A digital pen is used for specialized input, like drawing or writing on touchscreen devices, but it is not typically required for a standard webinar.

D. Mouse: Similar to the keyboard, a mouse can help navigate, but it's not crucial to test for functionality in a webinar context.

F. Docking station: A docking station is a hardware peripheral that provides additional ports and connectivity. While it might be useful, testing the docking station itself isn't necessary for ensuring a successful webinar.

H. Monitor: A monitor allows the user to view the content, but it typically does not need to be specifically tested in a webinar application. The focus should be on audio and video components.

These components fall under the Mobile Devices and Peripheral Hardware domain of the CompTIA A+ Core 1 exam​​.