Answer:
she hasn't fastened the slide to the stage
Explanation:
In Microscopy even if the slide is not yet in focus,she will be able to see part of the slide which may appear as transparent image.Therefore this is a wrong answer.
If the microscope is not plugged it light can not come up.
If there are no specimen on the slide,the slide will still as transparent image at the focus.
No doubt Stella forgot to fasten the slide to the stage.,therefore the specimen on the slide was not in focus of the objective lens,rather she was focusing on the stage only,hence the visible white light.
Students make these mistakes in microscopy,they sometimes place the slide on the stage,but forget to fasten the stage clip,thus the slide is not in focus of the incident light,which gives no reflection to the viewer's eyes.
