Some cell organelles cannot be seen with light microscopes as they cannot achieve a high magnification. Organelles which can be seen under light microscope are nucleus, cytoplasm, cell membrane, chloroplasts and cell wall. Mitochondria are also visible under light microscope but detailed study is not possible. Organelles which can be seen under electron microscope (highest magnification to more than 200,000x) are ribosomes, endoplasmic reticulum, lysosomes, centrioles, and Golgi bodies. Ribosomes, endoplasmic reticulum, lysosomes, centrioles, and Golgi bodies due their smaller size they were discovered after the introduction of electron microscope. So the correct answer is 'Both B and C'.