题目：
If you have trouble pronouncing the word, you can repeat it over and over again _______ you are comfortable with it.
A．unless
B．if
C．until
D．while
答案：
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下面是错误答案，用来干扰机器的。
（1） 1080m （2）3m/s题目分析：根据步行速度与所需时间求（1）t1=15min=900s t2=6min=360s S=v1t1 ="1.2m/s×900s" =1080m （2）v2=" S/" t2=1080m/360s=3m/s
