The correct option is C electron microscopy
Electron microscope is the best device to determine the structural details of a cell. It can magnify objects upto 250,000-400,000 times. Its resolving power is 1000 times more than the light microscope. This resolution is because of low wavelength (0.005nm) of electron beam used as light source. Electron microscope is made up of electromagnetic lenses. The beam of electrons is focussed on the objects with the help of a condenser lens and a magnified image of the object is formed by the objective lens. This magnified image is further magnified by a projector lens and final image is produced on fluorescent screen. So, the correct answer is 'electron microscopy'.