It Has Been Hypothesised That Fungi and Plants Have a Mutualistic

It has been hypothesised that fungi and plants have a mutualistic relationship because plants make sugars available for the fungi's use. What is the best evidence in support of this hypothesis?

A) Fungi survive better when they are associated with plants.
B) Radioactively labelled sugars produced by plants eventually show up in the fungi with which they are associated.
C) Fungi associated with plants have the ability to undergo photosynthesis and produce their own sugars, while those not associated with plants do not produce their own sugars.
D) Radioactive labelling experiments show that plants pass crucial raw materials to the fungus for manufacturing sugars.