begin的变形属于不规则变化，begin的过去式和过去分词分别是began和begun。
例句：
He stood up and began to move around the room.
他站了起来，开始在屋子里走来走去。
The weight loss began to look more serious.
体重的减轻开始显得更严重。
"Professor Theron," he began, "I'm very pleased to see you."
“西伦教授，”他开始说道，“我非常高兴见到你。”
