Details of telephone charges can be found at the front of any telephone directory ( 电话簿), where you will see that the cost of your call will depend not only on the duration and distance but aim on what time of day the call is made and sometimes on whether or not it is made at the weekend or during the week. Between most places in Britain it is now possible to dial direct by STD ( Subscriber Trunk Dialing) (拥护直通长途电话). Charge rates are higher for calls made from coin - box phones and call offices than for those made from ordinary lines, and calls connected by the operator are normally more expensive than calls you dial direct.
STD facilities now exist between Britain and most countries in Western Europe and also with a number of other overseas countries beside. Other calls will require the assistance of the operator. Charge rates for international calls depend broadly on the same factors as for inland calls. Full details of international telephone charges and services are found in directories.
Transferred charge calls are those where the people you want to speak to agree to pay for your call to them. Personal calls are those where you tell the operator the name of the person you wish to speak to. You are not connected if that person cannot be found, though a message can be left for him or her to ring the operator later.
From most telephones, if you want the police, fire or ambulance services, dial 999. Tell the operator the service you want. Wait until the emergency authority answers. Then give them the full address where help is needed and other necessary information. 999 calls are free.Which of the following statements is true（）

A．STD works with operators.
B．STD is popular all over the world.
C．STD is popular only in West Europe.
D．STD works without operators.