A.fff\(\frac{7}{3}\)/fff-r
B.fff\(\frac{7}{3}\)/fff+r
C.7 − 3r
D.fff\(\frac{7}{3}\)/fff-fff\(\frac{r}{3}\)/fff
E.fff\(\frac{7}{3}\)/fff+fff\(\frac{r}{3}\)/fff
我的答案: