Dear Student
Statement A is right as when ball is dropped from height h, its velcoity is zero but acceleration due to gravity acts on it.

Statement B  is also right. In uniform motion velocity is constant ( non - zero) but acceleration is zero.
If speed of a particle is constant, its acceleration must be zero. This is wrong statement.
A constant speed does not imply that acceleration is zero. For example in circular motion, speed is constant but direction of motion changes continuously changes hence there is acceleration.

Regards

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