学习笔记：
★cat：猫
例句：The cat screwed every movement of the mouse. 猫注视着老鼠的每一个动作。
★dog：狗
例句：The dog is his master's shadow. 这条狗和主人形影不离。
★sidewalk：人行道
例句：The wall lay any which way between the bare yard and the broken sidewalk. 那墙弯弯曲曲地立在空院与破烂的人行道之间。
★wagon：小手推车
例句：The wagon must go whither the horses draw it. 马拉到哪里，车就得跟到哪里。
★letter：信
例句：Eyes speak all languages, wait for no letter of introduction. 眼睛能讲各种语言，他不需要介绍信。
