The correct answer is B. since.
The word “since” is used to indicate a point in time in the past from which something has continued or happened. In this case, the speaker is indicating that the person has been absent from a certain point in time, which is a fortnight ago.
The other options are not correct because they do not indicate a point in time in the past. The word “from” is used to indicate a starting point, but it does not indicate that something has continued or happened since that point. The word “for” is used to indicate a period of time, but it does not indicate that something has started at a specific point in time. The word “to” is used to indicate a destination or goal, but it does not indicate that something has happened since a specific point in time.