Assuming that a variable can hold only one value at a time, what will happen with the original value if it is replaced by a new variable.

a$)$ It will be stored as spam while the session is open.

b$)$ It stays accessible for a short time; it can be accessed by using Ctrl$+$Z$.$

c$)$ It is lost forever.

d$)$ It is not possible to replace the value assigned to a variable.