【单选题】
A <{p}><{font _mstmutation="1" _msthash="20496" _msttexthash="16089203"}>一定等于零<{/font}><{br/}><{/p}>
B <{p}><{font _mstmutation="1" _msthash="20500" _msttexthash="17222816"}>可能等于零<{/font}><{br/}><{/p}>
C <{p}><{font _mstmutation="1" _msthash="20497" _msttexthash="15066857"}>一定大于零<{/font}><{br/}><{/p}>
D <{p}><{font _mstmutation="1" _msthash="20501" _msttexthash="15153905"}>一定小于零<{/font}><{br/}><{/p}>
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