题目内容：
请根据短文内容，回答题。When you speak on the telephone。you cannot use your facial(面部的)expression，eye contact and gestures to help communicate your message．Your voice must do the job．
A good voice is pleasant to listen to because it communicates a positive message．Keep in mind the following qualities of a good voice.
Speak in a voice neither too loud nor too soft．Speak louder when giving important information.
Speak slowly enough so that the listener has a chance to understand your messages without your having to repeat it．Keep in mind that as you speak the other person may be taking notes.
Pronunciation is the correct way to say a word．To avoid mispronouncing(读错音)words，you may wish to check the pronunciation of unfamiliar words in the dictionary before you use them.
People with an accent unlike yours may not understand your pronunciation of some words. You also may not understand the pronunciation of some of their words．In these cases，careful pronunciation is very important for effective communication．You may need to repeat or spell words that are unusual or easy to be misunderstood．
When speaking on the phone，the essential factor for successful communication is your ______. A．voice
B．gesture
C．eye contact
D．facial expression
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