Question

two kinds of iron
the human body needs iron to produce hemoglobin, a substance that helps red blood cells transport oxygen. without enough iron, a person may feel tired and weak. dietary sources of iron include plant sources, such as vegetables and beans, and animal foods, including poultry, red meat, and fish. however, plant and animal sources are not equal. the iron in plants, called nonheme iron, is not easily absorbed by the human digestive system. for example, a half cup of cooked spinach contains a healthy dose of over three milligrams of iron. unfortunately, only five percent of that iron can be used by the body. on the other hand, the iron in animal foods, called heme iron, is better utilized. heme iron is contained within a ring of protein, which helps the body to absorb it easily.
what is the main, or central, idea of the passage?
plant and animal food sources both contain iron, but the iron in animal foods is more accessible to the body.
heme iron, found in meat and fish, is easily absorbed by the human body.
plant and animal food sources both contain iron, which helps red blood cells carry oxygen throughout the body.

Explanation:

1. Analyze the first option: The passage states that both plant and animal foods have iron, and then compares their absorption—plant iron (nonheme) is poorly absorbed, animal iron (heme) is better utilized. This matches the central idea of comparing iron from both sources and their accessibility.
2. Analyze the second option: This only focuses on heme iron, ignoring the plant iron part which is a key comparison in the passage. So it's too narrow.
3. Analyze the third option: This only mentions that both have iron and the role of iron, but misses the main comparison about absorption/accessibility which is a major part of the passage.

Answer:

A. Plant and animal food sources both contain iron, but the iron in animal foods is more accessible to the body.