Answer:
 B) that is free of microbes. 
Step-by-step explanation:
An axenic environment - 
It is the state of culture , where only a single type of organism , species or strain exist , without any contamination for any other species , is referred to as an axenic environment . 
It is a important tool, which is required to study the parasitic organisms in any restricted environment . 
Hence, from the question, 
The correct option regarding axenic environment is B) that is free of microbes.