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“This method of trading is safe, if not safer than giving credit card numbers over telephone.”可以译成“这种交易方法的安全性可能绝不亚于在电话上把信用卡的号码告诉别人的方法”。
if not
adverb
perhaps; indicating possibility of being more remarkable (greater or better or sooner) than; "will yield 10% if not more"; "pretty if not actually beautiful"; "let's meet tonight if not sooner"