It is given that we need to identify a necessarily true statement.
As there is no information of direction, therefore even though the particle’s speed is constant it can be accelerating. For example in a circular motion.
Acceleration depends on the velocity which in-turn depends on its magnitude and direction; therefore no condition can be applied on acceleration.
It could be that particle is moving in a straight line, therefore with a surety, we can’t say the particle is moving in a circular direction.
But, acceleration will always be in the plane of motion only.
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