Pick up the most stable carbanion.

Given data:
It is given to identify the most stable carbanion.
Explanation:
Alkyl groups are electron donating or releasing groups. They increases the electron density on carbanion and make it less stable. 

More is the number of alkyl group, more it leads towards instability. Among the given option, the most stable carbanion is the methyl anion, ${\mathrm{CH}}_3^{-}$ which has no alkyl groups.

Hence, the correct option is option (A) 

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