The truck was . . . . . . . the traffic and the policeman asked the driver to move off.

The correct answer is B. obstructing.

The truck was obstructing the traffic, which means it was blocking the way of other vehicles. This is a dangerous situation, as it can cause accidents. The policeman asked the driver to move off so that the traffic could flow freely.

The other options are not correct.

• Failing: The truck was not failing to do anything. It was simply blocking the way of other vehicles.
• Obviating: The truck was not obviating the traffic. Obviate means to make something unnecessary or irrelevant. In this case, the truck was making the traffic necessary, not unnecessary.
• Hiding: The truck was not hiding. It was blocking the view of other drivers, but it was not hidden itself.
• Disturbing: The truck was not disturbing the traffic. It was simply blocking the way of other vehicles.

I hope this explanation is helpful!