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| obedient | 
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| a.  (服从的,顺从的) subject in will or act to authority; willing to obey; submissive to restraint, control, or command | 
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| objective | 
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| a. Syn. fair (不为情所动的,公平的,客观的) not influenced by emotions; having actual existence or reality | 
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| obligated | 
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| a. Syn. required; responsible (有义务的,有责任的) required; responsible; under a moral obligation to someone | 
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| obligatory | 
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| a. Syn. required (必须的) morally or legally constraining; required; binding | 
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| oblige | 
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| v. Syn. force; compel; coerce (迫使,责成) force; bind by an obligation; cause to be indebted; do a service or favor for | 
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| oblivious | 
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| a. Syn. forgetful (遗忘的,出神的) inattentive or unmindful; lacking all memory; forgetful | 
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| obscene | 
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| n.  (淫秽的) offensive to accepted standards of decency or modesty; repulsive; disgusting | 
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| obscure | 
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| v. Syn. darken; hide; block (使暗淡,使模糊,隐藏) darken; make dim or indistinct; conceal in obscurity | 
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| obsess | 
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| v. Syn. besiege (纠缠,困扰) preoccupy the mind of excessively; besiege; compass about; dominate the thoughts of someone | 
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| obsession | 
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| n. Syn. fascination; mania (入迷,固执的念头) compulsive, often unreasonable idea or emotion | 
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| obsolete | 
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| a. Syn. outmoded; antiquated (过时的,无用的) no longer useful; outmoded; antiquated | 
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| obstacle | 
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| n. Syn. obstruction; impediment; hindrance (障碍) one that opposes, stands in the way of, or holds up progress | 
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| obtain | 
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| v. Syn. acquire; get; procure; derive (得到) get hold of; gain possession of; acquire, in any way | 
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| occasional | 
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| a. Syn. random; incidental (偶然的,临时的) random; occurring from time to time; infrequent | 
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| occasionally | 
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| ad. Syn. sometimes; infrequently; irregularly (偶尔) now and then; from time to time; infrequently; irregularly |