📄 Because the size range of virions is from 10 to 400 nm in diameter, they cannot be seen using a bright-field (light) microscope. So, the correct choice is option B: 10 to 400 nm; bright-field (light).

Because the size range of virions is from _________blank in diameter, they cannot be seen using a _________blank microscope.
Multiple Choice
A. 10 to 400 cm; scanning electron microscope
B. 10 to 400 nm; bright-field (light)
C. 10 to 400 nm; electron
D. 10 to 400 pm; bright-field (light) microscope