Answer:
"D"
Step-by-step explanation:
Conference call is a type of telephone call arrangement where a caller is able to connect and speak with several people at the same time. Its purpose is to beak distance barriers in communication and also fasten decision making process. Cost are also reduced through savings made on transportation cost.
For it to be effective , it is guided by a set of rules or etiquette.
One of such is that the area code and number of each person to be called should be available before contacting the call operator.