In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.

[Q]: Question: How many pathways do plants have for carbon fixation? Answer: three
[A]: Three many pathways do plants have for carbon fixation.

[Q]: Question: What is one problem with current methods of aluminum production? Answer: environmental contaminants
[A]: Environmental contaminants is one problem with current methods of aluminum production.

[Q]: Question: Sodium-potassium pumps help nerve cells establish a voltage across their what? Answer: plasma membranes
[A]:
Sodium-potassium pumps help nerve cells establish a voltage across their plasma membranes.