【单选题】 A B <{p}><{font _mstmutation="1" _msttexthash="98085" _msthash="72"}>F1+F3= F4-F2<{/font}><{br/}><{/p}> C <{p}><{font _mstmutation="1" _msttexthash="109473" _msthash="84"}>.F1= F2+F3+F4<{/font}><{br/}><{/p}> D <{p}><{font _mstmutation="1" _msttexthash="97812" _msthash="131"}>F1+F2=F3+F4<{/font}><{br/}><{/p}>
