The answer is Level 3 for this question.
To explain in full detail, it means that when a person tries to access something there is a kernel that starts that enforces the authorization rule. If the proper rule and information is supplied, one might be able to get past the security. If they do not then the person will be stopped. This is why security is important. With security, one is kept out that does not have the access.
- Day to day business
A company needs to have certain access levels in order to do their work day to day. This is why there are different security levels such as Level 3 for the answer to this question. This level allows a person to do day to day work, without getting into an area where they have restricted access. The daily work is done, but the more secure items are not provided to people without the access.
MAC traditionally uses a multi level secure system of MLS. This is the level mentioned above. The MLS is the actual structure one uses to determine where the security should be for the day to day running or other operations. Some may refer to the process and the subject as Orange Book as this defines the MAC and the restrictions on access.