大学英语：imitator: n 模仿者，联想：imitate: v 模仿;imitation : n 模仿

　　4. imitator: n 模仿者，联想：imitate: v 模仿;imitation : n 模仿

　　5. limitless : a 无限制的，与其同根的常见词汇：limit : n 极限，v 限定;limited ; a 有限的，limitation: n 局限

　　1). His knowledge about insurance is rather ______.

　　2). His energy seems to have no ____.

　　3). A wise man knows his ____.

　　4). In front of the ____ ocean, he found he was rather insignificant.

　　Answers: limited, limits, limitation, limitless.

　　6. penetrating: a 穿透的，贯穿的，动词：penetrate; 名词：penetration

　　7. participant: n 参加者，参与者，与其同根的常见词汇：participate: v, participation : n 固定搭配：participate in sth.