A. Return to the low-power magnification, refocus on the object, then return to the high-power lens is most likely to resolve the issue.
This is helpful because you only need to use the fine adjustment on the high-power lens to see the object clearly once it is clear under low power.
Even though using lens-cleaning paper to clean the lens should help, getting the right focus at low power is important, so the second option is not the right choice. Because you typically use the Fine adjustment with high-power lenses and the coarse adjustment with low-power lenses, the third option is incorrect. The final choice would also be wrong because if you can focus with a low-power lens, there is nothing wrong with the slide.
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