A. This depends on the gap and the 2 teeth either side.
If they are healthy teeth, unfilled, then drilling them down for a bridge is unwise as this will weaken them. If they are already heavily filled or crowned then you may consider the bridge to be the best option.
As a general rule if you have enough bone then an implant will be the best long-term solution as an implant is independent from the other teeth and stimulates the bone.