If the CACHE or NOCACHE options aren$$t included in the CREATE SEQUENCE command, which of the following statements is correct?

a$.$ Oracle $12$c generates $20$ integers automatically and stores them in memory.

b$.$ No integers are cached by default.

c$.$ Only one integer is cached at a time.

d$.$ The command will fail.

e$.$ Oracle $12$c generates $20$ three$-$digit decimal numbers automatically and stores them in memory.