(

x

2

-

1

3 x

)8展开式的通项为Tr+1=

C

r8

(

x

2

)8-r(-

1

3 x

)r=(-1)r(

1

2

)8-r

C

r8

x8-r-

1

3

r=(-1)r(

1

2

)8-r

C

r8

x8-

4

3

r

令8-

4

3

r=0，r=6，T7=(-1)6(

1

2

)8-6

C

68

=7

故选A