A、A leaking gas pipe. B、A house fire. C、A terrorist attack. D、A bomb. A事实细节题。短文最后一段提到：the explosion had been caused by a leaking

The Roberts were driving through Port Merlin when they’ heard a loud explosion. At first they thought it was the noise of a plane but before long they saw smoke using a few blocks away and a little further on they came upon a crowd in the street and men with armbands directing the traffic. The way ahead was blocked and they were in a one-way street, so they tried taking a short cut down a side street and soon found themselves in a bad traffic jam. The car in front of them stopped and couldn’t start again, so Mr. Robert helped the driver to push it ont of the way.
    In the meantime two fire engines as well as ambulances and police arrived and the ambulance men began looking for victims among the debris. The police put up a barrier with a notice across the street leading to the building, which was badly damaged, and tried to stop sightseers from getting near. Two of the ambulance men heard noises while they were searching. It sounded like someone knocking, so they took it in turn to clear away some bricks to get at the person under the floor beneath them. In the end they succeeded in rescuing him.
    Some of those who had narrow escapes were interviewed by press reporter. Apparently the explosion had been caused by a leaking gas pipe and it looked as if the firm which had recently fitted the pipes was responsible for the accident.