1、
Yes and how many times must cannonballs fly, Before they're forever banned?
炮弹要掠过天空多少回, 它们才被永远禁用?
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2、
'Thus for steel cannonballs, skipping can only occur for angles shallower than seven degrees.'
因此，对于钢制炮弹而言，只有投掷角度小于7时才有可能产生弹跳。
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3、
