Correct Answer - C
To find the base strength of carbanions, we consider the corresponding conjugate acids. The order of their acidic strength is
`C-=underset(sp)CHgtCH_(2)=underset(sp^(2))CH_(2)gtCH_(3)-underset(sp^(3))CH_(3)`
Thus, the order of base strength is just the reverse of it:
`CH_(3)barCH_(2)gt CH_(2)=barCH gt CH-=barC`