Just last week, familiar questions were starting to surface again about 49ers receiver A.J. Jenkins.With a sore right hamstring, the second-year wide receiver was sidelined at the team's Santa Clara training camp at a time when the Niners were hoping he could step up his performance in practices and showt he has what it takes to win a starting spot opposite Anquan Boldin.Because Jenkins essentially disappeared last season – failing to catch a single pass in the regular season – suddenly 49ers observers were wondering if the injury again might delay his development and leave him out of the picture. All those offseason stories about Jenkins putting in extra work with quarterback Colin Kaepernick or increasing his upper-body strength suddenly seemed irrelevant.After all, even Jenkins went into training camp knowing he had to prove himself."I don't want to have another slow year," he told the San Francisco Chronicle's Kevin Lynch.Now, Jenkins appears back on track.After returning to practice this weekend, Jenkins made an immediate impact – making a nice, 50-yard reception for a touchdown in practice Sunday – and showing the speed that caught the 49ers' eyes in...