The correct answer is the application of the coarse adjustment to focus the specimen under high power.
One should always remember while using the coarse adjustment to focus the microscope is to use it only with the low power objective. One should prevent the use of coarse adjustment when focusing on high power because the image moves in and out of focus too prompt that it becomes tough to accurately adjust the focus.
Secondly, one may run the threat of crashing the objective into the slide, that is, why it is recommended to use the coarse focus only with the 4x low power objective. However, one can use the fine focus knob with all the objectives.
