How did pasteur solve spallanzani’s problem of limiting exposure to air?

Pasteur solved Spallanzani’s problem of limiting exposure to air by using a flask with bent neck which allowed air to pass but did not allow microorganisms which are present in the air to reach the broth.

Pasteur was a scientist who was a pioneer of the process of pasteurization, in which we prevent liquids most importantly milk is heated to prevent spoiling due to bacteria.

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.