Answer:
A. an email.
B. You can respond immediately to what the person is saying.
Step-by-step explanation:
An email is a digital message which sent to communicate something via network. Emails are less responsive than an instant message. The emails are suitable mostly for office and are a formal mode of communication. An instant message is easy and fast which enables quick two-way feedback. A person can respond immediately to the text message when it is received making instant messages a rapid mode.