Answer:
A. The speed is unchanged.
Explanation:
In the case when the work is to be done on a particle i.e. zero so the change made in KE of the particle would be zero. This represent the work energy theroem. But when the KE remains same or does not change so it should be the same and the particle speed would also the same
Therefore as per the given statement, the first option is correct
And rest of the options are wrong