在下列各句的每个空格内填上一个适当的、完整的单词，该词的首字母已给。
Tom felt too sleepy to keep a____ in history class.
 I can't follow you. Can you e_____  it to me again?
Mary is s____  to be a good learner. Everyone thinks so.
Last month 10 persons were killed in the traffic a _____ .
He never does anything at home. He isn't a h____  boy. He's a lazy boy.

下丘脑中的热敏神经元在温度上升时冲动频率增加，冷敏神经元在温度下降时冲动频率增加，引起机体的散热和产热以维待体温的相对稳定．冷敏伸经元的冲动频率和热敏神经元的冲动频率相等时，机体的产热和散热达到平衡，回答下列问题：

（1）冬泳爱好者入水时，冷敏神经元的冲动频率____ （填“大于”“等于”或“小于”）热敏神经元的冲动频率．从而刺激机体增加____ ，以维持体温的相对稳定．冬泳爱好者冬泳时容易出现脸部发白的现象，其原因是寒冷刺激导致皮肤的毛细血管____ ．

（2）处于室内时，冷敏神经元的冲动频率____ （填“大于”“等于”或“小于”）热敏神经元的冲动频率．

（3）进入寒冷环境时，下丘脑分泌的____激素通过垂体促进甲状腺分泌甲状腺激素，同时机体出汗减少，将导致垂体释放的抗利尿激素____

如图中的甲和乙是两种声音的波形图，从图形可知：图 ____是乐音的波形．