Explanation:

- Option 1: Since

- Correct usage as it indicates a time period starting from when the special package was announced.

- It connects the joining of service with the timeline since the package initiation.

- Correct Answer

- Option 2: For

- Typically used to indicate the reason or purpose, not fitting well in the context of time.

- It doesn't accurately connect a timeline of events.

- Option 3: As

- Conveys reason or cause, similar to "because," but does not establish a clear time sequence.

- Doesn't specify the ongoing nature since a particular point.

- Option 4: Due

- Usually followed by "to" to indicate reason or cause.

- It doesn't imply anything about the timing or sequence.