Why Doesn't a Flatworm Have a Circulatory System

question 1

Multiple Choice

Why doesn't a flatworm have a circulatory system?

• A) The animal is flat enough to permit effective gas exchange by diffusion.
• B) There is not enough room for a circulatory system.
• C) The animal lacks muscles, so it could not have a heart to pump blood.
• D) Only bilaterally symmetrical animals need a circulatory system.
• E) Only vertebrates have circulatory systems.

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