Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: Today, nearly 400 animals are listed as threatened or endangered animals in the United States. Many are at risk of becoming extinct or disappearing permanently. Unless efforts to save these vulnerable animals succeed, many of the country's greatest creatures will be lost forever. From the facts listed, guess which animals are endangered. Click on the picture to find out more about each of these animals in trouble. American Crocodile *American crocodiles are about 12 feet long. They live on land and in shallow water, swamps and marshes. *American crocodiles like to float in the water with only their eyes and noses above the water surface. *American crocodiles eat mostly small animals, which they grab with their strong jaws and sharp teeth. *American crocodiles lay eggs. They hide their eggs under twigs and leaves, or bury them in the sand. *Some crocodiles help their young hatch, and then carry them to the water in their mouth. Habitat Southern Florida, Mexico, Central and South American, Caribbean islands. Why It's Endangered Overhunted for its skin and habitat destruction. Peninsular Bighorn Sheep *Bighorn sheep can weigh as much as 280 pounds and stand about 3 feet tall. *They live in dry, desert mountain ranges, near rocky cliffs. *Bighorn sheep eat grass, twigs and leaves. *Male sheep are called rams and can be recognized by their huge, brown horns. The horns curl back over the ears, down,and up past the cheeks. *They live in herds or groups. The male sheep with the biggest horns are usually in charge. Male horns can weigh as much as 30 pounds. *Males will use their massive horns to fight. The fights can last as long as 24 hours. *Females are called ewes. They are smaller than rams and have shorter, smaller horns. Habitat Nevada and California to west Texas and south into Mexico. Why It's Endangered Loss of habitat, hunting illegally, drought and disease. 
 Question: Where can we find both American crocodiles and Bighorn sheep according to the passage?
mexico.

Context: During active transport, molecules move from an area of low concentration to an area of high concentration. This is the opposite of diffusion, and these molecules are said to flow against their concentration gradient. Active transport is called "active" because this type of transport requires energy to move molecules. ATP is the most common source of energy for active transport. As molecules are moving against their concentration gradients, active transport cannot occur without assistance. A carrier protein is always required in this process. Like facilitated diffusion, a protein in the membrane carries the molecules across the membrane, except this protein moves the molecules from a low concentration to a high concentration. These proteins are often called "pumps" because they use energy to pump the molecules across the membrane. There are many cells in your body that use pumps to move molecules. For example, your nerve cells (neurons) would not send messages to your brain unless you had protein pumps moving molecules by active transport. The sodium-potassium pump ( Figure 1.1) is an example of an active transport pump. The sodium-potassium pump uses ATP to move three sodium (Na+ ) ions and two potassium (K+ ) ions to where they are already highly concentrated. Sodium ions move out of the cell, and potassium ions move into the cell. How do these ions then return to their original positions? As the ions now can flow down their concentration gradients, facilitated diffusion returns the ions to their original positions either inside or outside the cell. 
 Question: which statement is true concerning active transport?
during active transport, molecules move from an area of low concentration to

Context: An electric transformer is a device that uses electromagnetic induction to change the voltage of electric current. Electromagnetic induction is the process of generating current with a magnetic field. It occurs when a magnetic field and electric conductor, such as a coil of wire, move relative to one another. A transformer may either increase or decrease voltage. You can see the basic components of an electric transformer in the Figure 1.1. Click image to the left or use the URL below. URL: The transformer in the diagram consists of two wire coils wrapped around an iron core. Each coil is part of a different circuit. When alternating current passes through coil P, it magnetizes the iron core. Because the current is alternating, the magnetic field of the iron core keeps reversing. This is where electromagnetic induction comes in. The changing magnetic field induces alternating current in coil S of the other circuit. Notice that coil P and coil S in the Figure 1.1 have the same number of turns of wire. In this case, the voltages of the primary and secondary currents are the same. Usually, the two coils of a transformer have different numbers of turns. In that case, the voltages of the two currents are different. When coil S has more turns than coil P, the voltage in the secondary current is greater than the voltage in the primary current (see Figure 1.2). This type of transformer is called a step-up transformer. Thats because it steps up, or increases, the voltage. When coil S has fewer turns of wire than coil P, the voltage in the secondary current is less than the voltage in the primary current (see Figure 1.3). This type of transformer is called a step-down transformer because it steps down, or decreases, the voltage. Q: Both step-up and step-down transformers are used in the electrical grid that carries electricity from a power plant to your home. Where in the grid do you think step-down transformers might be used? A: One place that step-down transformers are used is on the electric poles that supply current to homes. They reduce the voltage of the electric current before it enters home circuits. 
 Question: an electric transformer contains

an iron core.