Final answer:
For a subway train moving to the left with a negative velocity to come to a stop, the direction of acceleration is to the right and its sign is positive, making the correct answer option c) Right, positive.
Step-by-step explanation:
If a subway train is moving to the left, which indicates a negative velocity, and then comes to a stop, it is experiencing deceleration. Deceleration refers to acceleration in the direction opposite to the direction of velocity. Since the velocity is negative (to the left), the acceleration must be in the opposite direction, which is to the right. For the train to come to a stop, the acceleration must be positive to reduce the magnitude of the negative velocity. Thus, the direction of its acceleration is to the right, and the acceleration is positive.
Additionally, in terms of one-dimensional motion, plus and minus signs are used to indicate direction. The sign of an acceleration that reduces the magnitude of a negative velocity is positive. Conversely, to reduce the magnitude of a positive velocity, the acceleration sign would be negative.
Therefore, the correct answer to the question is option c) Right, positive, as this reflects the direction and sign of the acceleration when the train decelerates to come to a halt, moving from a negative velocity to zero.