Ask anyone what’s different about the 2017-18 Boston Bruins and they’ll tell you that a talented rookie class and a new coach is sparking their run over the last 21 games.

Those two assets are true, but one thing, in particular, that’s sticking out compared to the last three years, is forward depth. All four lines are finding ways to contribute both on and off the scoresheet over the last month.

Case in point the pair of wins over the Senators and their win over the Islanders Tuesday night. The Bruins put up a five-spot in each of those victories. Only three of those 15 goals came from the top trio of Brad Marchand, Patrice Bergeron and David Pastrnak.

The third and fourth lines, in particular, have led the way in the offensive output. Danton Heinen, Riley Nash and David Backes accounted for five goals while the Noel Acciari, Tim Schaller and Sean Kuraly trio lit the lamp three times – including twice in Brooklyn.

Not only are they contributing, but they are evening out the ice time. Instead of relying on the Bergeron line for over 20 minutes a night, the second, third and fourth lines are cutting into the time on ice numbers, thus giving Bruce Cassidy and his coaching staff a chance to roll out any trio throughout all 60 minutes.

Spreading out the ice time will only benefit the Bruins in the 82-game grind.

“Having games like [Tuesday in Brooklyn] and in Ottawa allows us to push the envelope a little bit, and I think it’s very important,” Cassidy assessed following practice at Warrior Ice Arena Wednesday. “The schedule the way it is, we’re playing and playing [often] and then we get a break next week to recharge, but then we’re back playing.

“I think it’s a credit to a lot of the guys in the room. [The Bergeron line] will be playing a lot down the road, but that’s the way we look at it.”

The Bruins aren’t just producing offensively, either.

Tuukka Rask (11-0-1 in his last 12 starts) is quieting his doubters after notching NHL first star of the month honors. The defense is clearing out rebounds and establishing layers in front of Rask, two things they failed to accomplish on a regular basis in the first month of the season.

Both the power play — 12-for-48 in December — and penalty kill units are getting the job done giving the Bruins an edge at even strength and special teams.

“When you got all four lines going and it’s not just Bergy’s [Bergeron’s] line that’s producing, [then] other teams can’t just load up a line or load up their best checking pair against Bergy’s line and shut them down,” Backes, the NHL’s reigning third star of the week, said.

“Now it’s four lines producing and it’s a headache for other teams to try to find out a game plan on who they’re going to stop. If they want to stop Bergy’s line and they want to put all their apples into that basket then we need other guys producing, and we have.”

Even with just three goals — two coming Tuesday — the Bergeron line is shutting down top scoring lines across the ice. They’re getting their share of chances but haven’t found the back of the net as frequently.

One player, in particular, Pastrnak, hasn’t scored in 10 straight games. The 2014 first rounder has seven assists in that span and is making strides toward becoming a 200-foot player.

At the very least, Pastrnak is bringing his ‘B’ game, and that’s not a bad thing.

“[Pastrnak] falls on the offensive side where he has some assists and is contributing five-on-five,” Cassidy said. “We’re happy for David. Obviously, we’d like him to score, but he hasn’t hurt us and he’s still making plays.”

The Bruins are making plenty of plays and trending toward the top of the Eastern Conference. They sit two points ahead of the Toronto Maple Leafs for second place in the Atlantic Division — with two games in hand.

And acing Cassidy’s tests.

“You take a look around the room and it seems like we’re getting, you know, those ‘A’ and ‘B’ games — and none of those ‘C’ games where guys are off,” Cassidy added. “If they’re not on the scoresheet, they’re doing something to help you win.”