表达玩耍的快乐：have fun等 — 英语填空题
题目
根据语境和中文提示，用所给词的适当形式补全句子（每空一词）。Yesterday was Linda's birthday. She invited her friends to the park. They played games, sang songs and ate cakes together. They really ___ ___（玩得开心）there. 注意：句中有 yesterday，动词形式要与之保持一致。