题目

Do you ever practice playing the piano in your mind by tapping on imaginary black and white keys when you have no piano in front of you? It’s not unusual--great pianists like Polish-American Arthur Rubinstein sometimes used to practice in their minds. For more than 100 years, scientists have been trying to understand how this mental training works. In the 1930s, researchers showed that when you’re imagining an action, your brain sends signals to your muscles that are too weak to make the muscles move but might help train the body to perform. Practicing in your head might also create11、a6÷a2×a3=a7．