问题
选择题
23. Speed of cars is measured ________kilometres per hour.
A．on
B．in
C．by
D．to
答案
答案：B
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23. Speed of cars is measured ________kilometres per hour.
A．on
B．in
C．by
D．to
答案：B
缺失，缺牙间隙已明显缩小，拟采用哪种间隙保持器最为合适（）