A.b =fff\(\frac{a}{3}-\frac{2}{3}\)/fff
B.b =fff\(\frac{a}{3}-\frac{2}{x}\)/fff
C.b =fff\(\frac{a}{3}-2\)/fff
D.b = a −b =fff\(\frac{2}{3}\)/fff
E.b = a +fff\(\frac{2}{3}\)/fff
我的答案：
