How are POP$3$ and IMAP$4$ different?

Question $25$ options:

a$)$

POP$3$ can only be accessed from one computer where IMAP$4$ can be accessed from multiple computers

b$)$

IMAP$4$ can only be accessed from one computer where POP$3$ can be accessed from multiple computers

c$)$

POP$3$ is the sending of email from one server to another where IMAP$4$ is the storing and retrieving of incoming email messages

d$)$

IMAP$4$ is the sending of email from one server to another where POP$3$ is the storing and retrieving of incoming email messages