Câu hỏi:

Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions.

     There are some unattended level crossings, with gates which road-users have to open themselves, 'Stop' signs, and small red and green lights. Do not cross when the red light is showing, as a train is coming. There is a special railway telephone, and if you are driving a very large or slow moving vehicle, or are on foot with animals, you must first telephone the nearest station to make sure it is safe for you to cross. Open both gates before you cross and close them after you. When you have crossed, telephone the station to let them know you are over.

     Some other unattended level crossings have gates but have no red lights. At such crossings, stop, look both ways, listen and make sure there is no train coming. If there is a special railway telephone, first telephone to make sure it is safe for you to cross. Before you cross with a vehicle or with animals, open the gates on both sides wide, and then check once again that no train is coming. Drive your vehicle or animals right across and well clear of the crossing and then close both gates.

All the level crossings described in the passage have_______.