Because the main difference between temporary seal and permanent seal is that temporary seal is sealed by water seal, while permanent seal is sealed by resin, no matter how backward the microscope is, water will not overflow from the permanent seal; However, there will be a lot of water in the process of making temporary films, such as dripping and dyeing. If the microscope is tilted, water will overflow and pollute the stage or test bed, which will affect the observation.

So choose d