Greg enjoys playing with his friends. On Friday, Greg went outside to play with two of his friends, Peter and Lucy. They played with a ball for some time, but then they got bored. Lucy said that she wanted to climb a tree. Peter thought that they could see if their other friend Robert could play with them.  The three of them went to find Robert. They saw Robert in front of his house, but he said that he was busy and he could not play with them. Greg and Peter then thought that Lucy's idea was good. There was a large tree in the park. Greg, Peter, and Lucy walked to the park together.  When they got to the park, they were surprised by the size of the tree. It was much larger than they thought. At first, Greg was scared to climb the tree. But Peter and Lucy told him that it would be fun, so he began to climb. When he had climbed the first few branches, he slipped and fell down. But he was not hurt. After that, the three friends thought that it was too dangerous to climb that tree. So they all went home.  When Greg went home, his mother asked him what happened. She saw that his shirt was dirty. Greg explained about the tree. Then he changed into a different shirt, so that his mother could wash the dirty shirt. What was the name of Greg's friend who could not play with them?
Peter Greg Lucy Robert
Question: Greg enjoys playing with his friends. On Friday, Greg went outside to play with two of his friends, Peter and Lucy. They played with a ball for some time, but then they got bored. Lucy said that she wanted to climb a tree. Peter thought that they could see if their other friend Robert could play with them.  The three of them went to find Robert. They saw Robert in front of his house, but he said that he was busy and he could not play with them. Greg and Peter then thought that Lucy's idea was good. There was a large tree in the park. Greg, Peter, and Lucy walked to the park together.  When they got to the park, they were surprised by the size of the tree. It was much larger than they thought. At first, Greg was scared to climb the tree. But Peter and Lucy told him that it would be fun, so he began to climb. When he had climbed the first few branches, he slipped and fell down. But he was not hurt. After that, the three friends thought that it was too dangerous to climb that tree. So they all went home.  When Greg went home, his mother asked him what happened. She saw that his shirt was dirty. Greg explained about the tree. Then he changed into a different shirt, so that his mother could wash the dirty shirt. What was the name of Greg's friend who could not play with them?
A. Peter
B. Greg
C. Lucy
D. Robert
Answer: