Q: Premise: "Two elder men sitting under a tree."
Hypothesis: "Two men sit by a tree."
Do we know that the hypothesis entailed by the premise?
A: Sitting under a tree can be rephrased as to sit by a tree.
The answer is yes.

Q: Premise: "A man dressed in red and black winter gear is airborne after hitting a jump on his snowboard."
Hypothesis: "The man is practicing for the winter games."
Do we know that the hypothesis entailed by the premise?
A: A man hitting a jump on his snowboard doesn't imply that he is practicing for the winter games.
The answer is it is not possible to tell.

Q: Premise: "A group of friends ride the current in a raft."
Hypothesis: "A group of friends ride in a raft."
Do we know that the hypothesis entailed by the premise?
A: The current does not stop a group from taking a ride in a raft.
The answer is yes.

Q: Premise: "A skier going down the snowy hill."
Hypothesis: "A snowboarder demonstrating downhill skills."
Do we know that the hypothesis entailed by the premise?
A:
A skier is different than a snowboarder and one is showing the action while the other is doing the action.
The answer is no.