A worker at a scrap metal yard had to move pieces of iron from one side of the yard to the other side of the yard using an electromagnet. After easily moving some of the smaller pieces of iron, he could not get a larger piece of iron to stay attracted to the electromagnet because it was too heavy. Since he is using an electromagnet, which of the following could he do to strengthen the electromagnet's magnetic field in order to lift the large piece of iron? Increase the electric current moving in the solenoid. O Use a smaller iron core. O Decrease the number of coils of wire in the solenoid. O He cannot change the electromagnet's strength.