Which of these vehicles must stop before crossing railroad tracks?

ANSWER:

Tank trucks marked with 'hazardous material placards' is the vehicle which must be stopped before crossing the railroad tracks.

EXPLANATION:

Basically, whenever the train is about to arrive or is about to pass, then all the vehicle must stop before crossing the rail road to prevent accidents.In this case, there are tanks with hazardous materials which may cause even more accident due to which the tank truck should be stopped before crossing the rail road.

The war began as a fight between mayans and the landowners of the country. the main causes of the guatemalan civil war was started by the greed of the united fruit company, the fear of communism, and the racism toward the  mayan  people.