2 Q's

[Ciberon]

1. Does Choke affect snow-covered lands?

2. Can stifle affect spells with replicate?

[Pastorofmuppets]

2. Can stifle affect spells with replicate?

If it says "When" or "Whenever" at the beginning of it, it can be Stifled.

[Valtrix]

Choke affects anything with an island subtype. For example, tropical island says land - island forest; likewise, snow-covered islands say basic snow land - island.

[Tacosnape]

Valtrix is right on the Choke.

As for the Stifle thing, "At" is also a triggered ability. And yes, you can Stifle Replicate. It's one of the only ways to get around Replicate's insane stupidity (It's seriously as broken a mechanic as Storm, they just haven't printed the cards to back it up.)