Q: Fact 1: Viruses are so small that they can be seen only with an electron microscope. Fact 2: Viruses are studied by radiography and use of the electron microscope. Given the two facts above, what is used to study viruses?

Available choices:
(1). rays or beams;
(2). Cooking;
(3). aqueous solution;
(4). energy;
(5). an image;
(6). radiation;
(7). radiography;
(8). Dilution;
A:
(7).