A

Step 1: Identify the forces acting on the pendulum bob when the train brakes. The pendulum must accelerate backward due to the deceleration of the train.
Step 2: By applying Newton's second law, the net force acting on the pendulum is the result of gravitational force and tension in the thread.
Step 3: Analyze the pendulum's motion and the angle at which the pendulum whips back when the train comes to a sudden stop. The pendulum requires sufficient energy to swing through 180 degrees.
Step 4: Considering the conservation of energy, if the pendulum gains enough kinetic energy from the braking force, it will successfully swing through 180 degrees.
Therefore, the answer is Yes, the pendulum can travel through 180º, allowing the taut thread to reach the vertical position.