Given the question: Answer the following question given this paragraph: The higher up a food chain that humans eat, the greater the levels of toxic metals they take in. That's why people should avoid eating too much of large fish such as tuna. Tuna are predators near the top of their food chains. They have been shown to contain high levels of mercury. In people, heavy metals can damage the brain and other organs. Unborn babies and young children are most affected. That's because their organs are still developing. Q: Tuna have been shown to contain high levels of what metal? Choices: - cadmium - titanium - iron - mercury A:
The answer is:
mercury