A microscope that is calibrated this way will maintain the specimen in focus when the objective lens is rotated. ● Pointer
● C-mount
●fine focus
●Parfocal

The correct option is;

Parfocal

Explanation:

A perfocal lens is one that when in use, the object remains in focus when the  objective lens is rotated to change the magnification power of the microscope. That is the when the magnification is adjusted, the objectives remains in focus. The use of the parfocal lens however results in a small but insignificant amount of error in the focus.

Excretory system is important to the proper functioning of the body as it removes all the waste materials, which if accumulated, can be toxic for the body. for instance, high levels of urea in blood can be hazardous for cells of the body. when the excretory system does not work well, it can lead to several diseases including kidney stones, nephritis, cystitis, etc.