题目

Last summer, as part of my high school graduation project, I volunteered at Saunders House nursing home. I choose this experience because it was something that I had never done before and I wanted to lend a helping hand．When I first came up with the idea of volunteering at a nursing home, I wanted to help out with activities and meet with some of the residents （住客）. At first it was challenging because I was extremely shy; however after getting to know the residents a little better, I started to feel more comfortable around them. My goal in volunteering was to bring a smile to 棱长为2的正方体ABCD-A1B1C1D1中，=（ ）A．B．4C．D．-4