Viruses can be seen with a(n):

Viruses are microscopic entities that fall below the resolution limits of standard light microscopes, which typically can resolve objects down to about 200 nanometers. In contrast, electron microscopes use electron beams to achieve much higher resolution, allowing for visualization of structures as small as 0.1 nanometers. This capability is essential for studying viruses, which generally range in size from about 20 to 300 nanometers.

The electron microscope's ability to produce magnified images of tiny particles gives researchers the necessary tool to investigate viral structures, such as capsids and envelopes, in detail. This is fundamental for virology research, diagnosis, and the development of vaccines and treatments. Other options like the magnifying glass, light microscope, and slit lamp lack the necessary resolution and functionality to visualize viruses directly.