What would be the best countermeasure to protect against such escalation?

Once an intruder has access to a remote system with a valid username and password, the attacker will attempt to increase his privileges by escalating the compromised account to one having increased privileges, such as that of an administrator. What would be the best countermeasure to protect against such escalation?

A.
Give users tokens

B.
Give user the least amount of privileges

C.
Give users a strong policy document

D.
Give users two passwords

Explanation:
With less privileges it is harder to increase the privileges.