Which of these characteristics best helps scientists classify organisms?
A: structure

A disorder is associated with certain flaws in the human respiratory system. Which is most likely a typical symptom of this disorder?
A: difficulty breathing

During a lab investigation a scientist heats a solid substance. The scientist observes that the solid has two different melting points. The scientist is able to separate the two resulting liquids. Which statement best classifies the original solid substance?
A: It was a mixture.

A manufacturer wants to produce a container for food storage that does not break easily and is airtight, inexpensive, and microwave-safe. Which of the following is the best material to use to make the container?
A:
plastic