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 idea of the passage?

"the children's hour" by henry wadsworth longfellow between the dark and the daylight, when the night is beginning to lower, comes a pause in the day's occupations, that is known as the children's hour. i hear in the chamber above me the patter of little feet, the sound of a door that is opened, and voices soft and sweet. from my study i see in the lamplight, descending the broad hall stair, grave alice, and laughing allegra, and edith with golden hair. a whisper, and then a silence: yet i know by their merry eyes they are plotting and planning together to take me by surprise. a sudden rush from the stairway, a sudden raid from the hall! by three doors left unguarded they enter my castle wall! they climb up into my turret o'er the arms and back of my chair; if i try to escape, they surround me; they seem to be everywhere. they almost devour me with kisses, their arms about me entwine, till i think of the bishop of bingen in his mouse-tower on the rhine! do you think, o blue-eyed banditti, because you have scaled the wall, such an old mustache as i am is not a match for you all! i have you fast in my fortress, and will not let you depart, but put you down into the dungeon in the round-tower of my heart. and there will i keep you forever, yes, forever and a day, till the walls shall crumble to ruin, and moulder in dust away! which literary device does longfellow use most frequently in the poem? a. simile b. metaphor c. repetition d. personification