A boy called Mario had many friends, and he was proud of it. Whoever he met, he would like to show off  how popular he was at school. One day, his grandpa said to him, "Mario, I know that you don't have as many friends as you think. Many of them are not true to you." Mario thought maybe his grandpa was right. However, he wasn't sure how he could test whether his schoolmates were real friends or not, so he asked his grandpa. The old man answered, "I have just exactly what you need. It's in my room. Wait a minute." The old man left, soon returning as if  carrying something in his hand, but Mario could see nothing there. "Take it. It's a very special chair. Because it's _ , it will be hard for you to sit on it. However, if you manage to sit on it, you can use the chair's magic power  to tell who your real friends are." Mario took the strange invisible chair to school. At break time he asked everyone to form a circle, and he put himself in the middle, with his chair. "Nobody move. You're about to see something amazing," said Mario. Then he tried sitting on the chair. Having difficulty seeing it, he missed and fell to the ground. Everyone had a pretty good laugh. "Wait, wait," said Mario, making another try. But again he missed the seat. Mario didn't give up. He kept trying to sit on the magic chair. Finally, he did it. This time he felt himself in mid-air. Then he experienced the magic that his grandpa had been talking about. Looking around, Mario saw George, Lucas and Diana holding him up, so he wouldn't fall. But some schoolmates whom he had regarded as friends had done nothing but made fun of him. Mario was quite thankful to his grandpa, who helped him test who his true friends were. Mario's grandpa gave him a special chair to   _  .
sit on in the school be his birthday present test who his true friends are play games with his friends at school