Question

multiple choice question
how did martinus beijerinck first reason that viruses were infectious agents?

using a bacterial filter
by mri and nmr
through a glycerol gradient
with a microscope

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Explanation:

Martinus Beijerinck used a bacterial filter (that traps bacteria) to show the infectious agent causing tobacco mosaic disease could pass through, concluding it was a non-bacterial, filterable infectious agent (virus). The other options are incorrect: MRI/NMR, glycerol gradients, and light microscopes were not used for this early virus research (viruses are too small for light microscopes, and the other techniques were developed much later).

Answer:

A. Using a bacterial filter