As they walk around a playground or other area, text, video or audio pops up at various points to help them try to figure out why aliens were in the schoolyard.
出自-2013年6月阅读原文
柯林斯高阶英汉双解学习词典释义
N-COUNT
(学校的)操场，运动场
The schoolyard is the large open area with a hard surface just outside a school building, where the schoolchildren can play and do other activities.