In the early days of germ theory, contagious diseases were thought to be caused by fungi or bacteria. In the 1980's, Dmitri Ivanovski filtered extracts from diseased tobacco plants and discovered that the disease could be transmitted to new plants through the filtrate. He concluded that the disease was caused by particles smaller than bacteria: the tobacco mosaic virus. Which best explains how Ivanovski's work led to a change in germ theory?
A. he tried to promote his hypothesis as a law.
B. he used a new experimental method to test his hypothesis.
C. he used a more powerful bacterial strain

Question

In the early days of germ theory, contagious diseases were thought to be caused by fungi or bacteria. In the 1980's, Dmitri Ivanovski filtered extracts from diseased tobacco plants and discovered that the disease could be transmitted to new plants through the filtrate. He concluded that the disease was caused by particles smaller than bacteria: the tobacco mosaic virus. Which best explains how Ivanovski's work led to a change in germ theory? 
A. he tried to promote his hypothesis as a law.
B. he used a new experimental method to test his hypothesis.
C. he used a more powerful bacterial strain