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: Which state of matter has the lowest density? Answer: gases
[A]: Gases have the lowest density.

[Q]: Question: What tissue system has neither dermal nor vascular tissues? Answer: ground tissue system
[A]: The ground tissue system has neither dermal nor vascular tissues.

[Q]: Question: Birds evolved from what type of ancestor? Answer: reptile
[A]:
Birds evolved from reptile ancestors.