you can't judge a book by its cover

cover ['kʌvɚ]

v. 遮盖;掩蔽;涉及;洒上; n. 覆盖物;避难所;掩护;封面;

judge [dʒʌdʒ]

vt.& vi. 审判，评判;断定; vt. 估计;评价;（尤指）批评;想，认为; n. 法官;裁判员;评判员;鉴定人;

book [bʊk]

n. 书;卷;课本;账簿; vt.& vi. 预订; vt. 登记;（向旅馆、饭店、戏院等）预约;立案（控告某人）;订立演出契约; adj. 书的;账簿上的;得之（或来自）书本的;按照（或依据）书本的;