Acceleration is zero only when the change in velocity is zero. Since the initial and final velocity is not given, option A is not correct as it uses the word ‘must’. Option B can be correct as it uses the word ‘may’.

Since the acceleration is zero from t=0 to t=10 s and initial velocity is zero, the change in velocity is zero and thus the final velocity is zero in this time interval. Therefore, the speed will also be zero in this interval. So, option C is correct.

Since speed is zero from t=0 to t=10 s and the initial velocity is zero, the final velocity will be zero and thus the change in velocity is zero in this time interval. Therefore, the acceleration will be zero in this interval. So, option D is correct.