Sip and zip， tip and dip， mop and nap are all__________.
A. minimal pairs
B. diphthongs
C. allophones
D. phonemes
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动能武器由发射装置、探测系统、瞄准系统、弹丸组成。()
If a teacher asks students to list as many ways as they can to tell someone to open the door and list the possible functions of a sentence in different contexts， he / she is probably trying to highlight__________.
A. the potential meanings of a sentence
B. different realizations of the same function
C. the relationship between form. and function
D. different ways of getting people to do the same thing
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