He has never _____such a strange thing. [ ]
A. hear
B. heard
C. hear of
D. heard of
答案:D
人民警察纪律,是指根据人民警察职业特点而制定的,要求人民警察在行使权利时必须遵守的义务性行为规范的总称。( )
根据等高距和等高线平距即可算出煤层的倾角。