Final answer:
Using the average size of a virus particle (around 100 nm), approximately 10,000 could fit in a 1-millimeter line, but considering smaller virions (20 nm), up to 50,000 could fit. Approximate answer given is 20,000 virions.
Step-by-step explanation:
To determine how many virus particles could fit along a 1-millimeter line, consider the size of virions. Most virions measure approximately 20 to 250 nanometers (nm) in diameter. Since 1 millimeter is equal to 1,000,000 nanometers, dividing 1,000,000 nm by the size of a virion gives an estimate of how many could fit end-to-end. Taking the average size of a virion to be about 100 nm, around 10,000 virions could fit along the line. However, since the smallest viruses are about 20 nm in size, up to 50,000 of these smaller virions might fit.
The correct answer is D) 20,000, since most virions are not as small as the smallest ones, and we are asked for an approximate number.