Which statement is an example of a requirement that is not well-formed?

Which statement is an example of a requirement that is not well-formed?

A.
The application should provide status messages every 60 seconds.

B.
The application user interface must be easy to use.

C.
The application must validate that the IP addresses that are input by users are valid IPv4
or IPv6 addresses.

D.
The application must be available for end users between 8am and 8pm EST/EDT,
Monday through Friday.

E.
The application should restart within 15 seconds.