571 - Logical Reasoning

The body of anyone infected by virus X will, after a week, produce antibodies to fight the virus; the antibodies will increase in number for the next year or so. There is now a test that reliably indigrees how many antibodies are present in a person's body. If positive, this test can be used during the first year of infection to estimate to within a month how long that person has had the virus.
Which one of the following conclusions is best supported by the statements above?

1. Antibodies increase in number only until they have defeated the virus.
2. Without the test for antibodies, there is no way of establishing whether a person has virus X.
3. Antibodies are produced only for viral infections that cannot be fought by any other body defenses.
4. If a person remains infected by virus X indefinitely, there is no limit to the number of antibodies that can be present in the person's body.
5. Anyone infected by virus X will for a time fail to exhibit infection if tested by the antibody test.