Answer:
Option B, Fix the piston in place so the volume of the pas remains constant
Explanation:
As we know

The effect on variable due to another variable can be studied by keeping the third variable constant.
Hence, in order the study the variation of temperature with pressure or vice versa, the volume needs to fixed at a certain value.
Hence, option B is correct
Answer: average annual rainfall, average annual temperatures, types of plants and animals native to the area
Explanation: the best way you can identify a biome is by telling which animal or species are native to the certain area